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Title: Validation of the repair effectiveness of mud grout injections by
lateral load testing of an adobe model building
Article Type: Research Paper
Keywords: adobe masonry; grouting repair; mud grout; horizontal loading;
static tests.
Corresponding Author: Dr. Ioannis Ioannou, PhD
Corresponding Author's Institution: University of Cyprus
First Author: Rogiros
Illampas
Order of Authors: Rogiros Illampas; Rui A Silva; Dimos C Charmpis; Paulo
B Lourenço; Ioannis Ioannou, PhD
Abstract: This study investigates the use of mud grout injections for the
repair of adobe masonry constructions. Relevant data from the literature
is reviewed, whilst the effectiveness of a laboratory-prepared mud grout
is assessed through an experimental program. A 1:2 scaled adobe model
building, previously subjected to a series of lateral loading cycles
resulting in significant cracking damage, was injected with the mud grout
and re-tested. The mix design of the mud grout was based on the use of
the same soil composing the earth masonry materials, hence ensuring
compatibility between repairing and original materials. Although the
grouting repair did not significantly alter the observed damage pattern
after re-testing, it generally succeeded in preventing failure
propagation through the injected crack paths. Furthermore, the injection
of mud grout showed to be a repair technique capable of partly restoring
the initial stiffness and load-bearing capacity of adobe masonry. The
high strength recovery ratios recorded under the tests using static
monotonic horizontal loading are particularly encouraging.
Suggested Reviewers: Marcial Blondet
Pontifical Catholic University of Peru
mblondet@pucp.pe
Professor of Civil Engineering. Specialist in earthquake engineering and
structural dynamics. Has ample experience in the experimental study of
the seismic behavior of structures. His main research interests are (i)
the development of low-cost solutions to mitigate the seismic risk of
non-engineered earthen and masonry dwellings, and (ii) the conservation
of earthen historical monuments in seismic areas.
Ioanna Papayianni
Aristotle University of Thessaloniki
papayian@civil.auth.gr
Professor of building materials. Research interest in materials and
methodologies for interventions in historic buildings and monuments.
Previous experience in earth masonry and mud grout injection design and
application.
Pete Walker
University of Bath
p.walker@bath.ac.uk
Chartered Civil Engineer. Director of the BRE Centre for Innovative
Construction Materials. His research interests include bio-based
construction materials, materials for improved indoor air quality and
structural masonry. Previous research experience in earth masonry.
Jean-Claude Morel
Coventry University
jean-claude.morel@coventry.ac.uk
Research Professor with an interest in sustainable buildings, notably
earthen structures (mechanical, hygrothermal and durability
characteristics of earthen stabilized or non-materials like adobe, rammed
earth, compressed earth blocks, earth mortar).
Lorenzo Miccoli
Bundesanstalt für Materialforschung und–prüfung (BAM)
lorenzo.miccoli@bam.de
PhD in Building Engineering and Architecture. Research interests in
structural engineering, materials testing, static analysis of historical
buildings and conservation engineering. Previous work on earth masonry
and grouts for the repair of earthen structures.
Cover Letter
P.O Box 20537, 1678 Nicosia
Tel: +357 22 892257
Fax: +357 22895318
Email: ioannis@ucy.ac.cy
www.ucy.ac.cy
5 February 2017
Prof. Michael C. Forde
Editor-in-Chief
Construction and Building Materials
Dear Prof. Forde,
We are submitting an unpublished paper, entitled “Validation of the repair effectiveness of mud
grout injections by lateral load testing of an adobe model building”, to be considered for
publication in Construction and Building Materials.
We believe our work is significant as it investigates the use of mud grout injections for the repair
of adobe masonry constructions through laboratory tests on a large scale specimen, namely a full
model of an adobe building. It is, therefore, our belief that this paper is well suited to Construction
and Building Materials, since it addresses a domain in which knowledge should be enhanced by
research work.
We look forward to your reply. Please note that you may address your correspondence to Ioannis
Ioannou (School of Engineering, University of Cyprus, 75 Kallipoleos Avenue, P.O. Box 20537, 1678
Nicosia, Cyprus; Tel: +357 22 892257; Fax: +357 22 895318; E-mail: ioannis@ucy.ac.cy).
Yours sincerely,
Ioannis Ioannou, Ph.D.
*Manuscript
Click here to view linked References
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Validation of the repair effectiveness of mud
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grout injections by lateral load testing of an
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adobe model building
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Rogiros Illampas1, Rui A. Silva2, Dimos C. Charmpis1, Paulo B. Lourenço2, Ioannis
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Ioannou1*
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Kallipoleos str., P.O. Box 20537, 1678 Nicosia, Cyprus
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Phone: +357 22892257
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Fax: +357 22895318
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Emails: rilamp01@ucy.ac.cy; charmpis@ucy.ac.cy; ioannis@ucy.ac.cy *
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URL: http://www.ucy.ac.cy/cee/en/
Department of Civil and Environmental Engineering, University of Cyprus, 75,
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4800-058 Guimarães, Portugal
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Phone: +351 253510200
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Fax: +351 253510217
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Emails: ruisilva@civil.uminho.pt; pbl@civil.uminho.pt
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URL: http://www.isise.net/
Department of Civil Engineering, ISISE, University of Minho, Campus de Azurém
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*Corresponding author
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Abstract
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This study investigates the use of mud grout injections for the repair of adobe masonry constructions.
26
Relevant data from the literature is reviewed, whilst the effectiveness of a laboratory-prepared mud
27
grout is assessed through an experimental program. A 1:2 scaled adobe model building, previously
28
subjected to a series of lateral loading cycles resulting in significant cracking damage, was injected
29
with the mud grout and re-tested. The mix design of the mud grout was based on the use of the same
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soil composing the earth masonry materials, hence ensuring compatibility between repairing and
31
original materials. Although the grouting repair did not significantly alter the observed damage pattern
32
after re-testing, it generally succeeded in preventing failure propagation through the injected crack
33
paths. Furthermore, the injection of mud grout showed to be a repair technique capable of partly
34
restoring the initial stiffness and load-bearing capacity of adobe masonry. The high strength recovery
35
ratios recorded under the tests using static monotonic horizontal loading are particularly encouraging.
36
Keywords
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Adobe masonry, grouting repair, mud grout, horizontal loading, static tests
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1. Introduction
Adobe bricks composed of unfired earth and, often, natural fibers have been
52
used for the construction of masonry since the Neolithic era (Morton, 2008; Houben
53
& Guillard, 1994). Nowadays, the use of adobe bricks for building contemporary
54
structures is limited, although efforts are currently in progress to develop sustainable
55
earth-based construction materials that fulfill modern-day requirements (Paul et
56
al., 2016). Nevertheless, a large stock of earthen buildings still exists in many parts of
57
the world and constitutes an important part of the international built cultural heritage.
58
Historic and vernacular adobe buildings are, in fact, also encountered in regions of
59
moderate to high seismic hazard such as the East Mediterranean, Southern Europe,
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North Africa, Middle East, South Asia and Central and South America.
61
Cyprus is among the countries of the Mediterranean basin with strong tradition
62
of building with adobe masonry. Local adobes have a characteristic slab-like shape
63
with typical dimensions of about (height x length x width) 5 x 45 x 30 cm3. Their
64
mechanical properties are rather variable due to the non-industrialized production
65
methods used (Illampas et al., 2014b), while the response of adobe assemblages
66
exhibits high deformability (Illampas et al., 2017).
67
Adobe bricks were extensively used in the lowland regions, urban centers and
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coastal areas of Cyprus until the mid-20th century (Illampas et al., 2011). Surviving
69
earthen structures range from simple single-roomed dwellings to elaborate urban
70
houses featuring stone supporting members (i.e. arches and buttresses) and timber
71
elements. Many of these constructions have been declared listed buildings or
72
monuments, and their protection is subsidized by governmental rehabilitation
73
schemes. Aiming at the preservation of their specific character, focus is being given
3
74
on the adoption of non-invasive intervention techniques that can efficiently restore
75
structural strength and stability.
(a)
(b)
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Figure 1. Cracks on adobe masonry walls in the mountainous village of Kakopetria (a) and in the
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coastal city of Limassol (b) in Cyprus.
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Despite the wide use and historic value of adobe masonry, experience has
79
shown its high vulnerability to cracking damage, due to its low tensile strength and
80
the quasi-brittle nature of its constituents (Fig. 1). As a result, adobe structures may
81
develop diagonal and/or vertical cracks even at relatively low levels of seismic action.
82
Foundation settlements and concentrated static loads can also induce cracking. The
83
presence of cracks poses a negative effect on the static and seismic behavior of adobe
84
masonry elements as they disrupt structural continuity, reduce the overall stiffness and
85
provide a path for damage propagation. Moreover, cracks promote moisture
86
penetration, which leads to water-mediated decay of the earthen materials, further
87
reducing their load-bearing capacity.
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Up to date, methods commonly used for repairing cracks in adobe masonry
89
structures included filling the gap with mortar, partial reconstruction of damaged
90
areas and stitching with timber/steel elements (Illampas et al., 2013). Questions are
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raised regarding the effectiveness of these techniques because certain interventions
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fail to reinstate monolithic behavior of the element, while others are considered
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excessively intrusive and costly as they involve considerable loss of fabric.
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Furthermore, installing materials much stiffer than adobe (e.g. steel or concrete) into
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cracked sections can result in adverse effects, since such interventions cause abnormal
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stress concentrations. Research has shown that grout injection is an alternative repair
97
solution with the capacity to provide adequate stiffness and strength recovery (Silva,
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2013). However, the development and validation of grouts incorporating earth in their
99
composition, in order to be compatible with adobe, remains a challenge.
100
In light of the above, this paper aims at investigating the effectiveness of the
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injection of mud grouts on the recovery of the load-bearing and deformation capacity
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of damaged adobe masonry constructions. For this purpose, a 1:2 scaled model of an
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existing adobe building from Cyprus was constructed and tested at the laboratory
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under monotonic static lateral loading. After subjecting the model building to a
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number of loading cycles that caused depletion of its overall stiffness and bearing
106
capacity, the resulted masonry cracks were injected with a laboratory-prepared mud
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grout and a new series of tests was undertaken. The structural behavior of the model
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before and after repair is hereby compared in terms of the recorded force-
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displacement response, damage distribution and failure mode. It is worth noting that
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this is one of the few studies that assess the effectiveness of mud grout injection
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through laboratory tests on a large scale specimen, namely a full model of an adobe
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building.
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2. Repair of earth constructions with grout injection
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Grouts are essentially fluid mortar mixtures that can be injected into cracks,
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fissures or gaps using gravity flow or pressure-assisted pumping. As the grout fills
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these voids and hardens, it provides adhesion between the masonry materials, re-
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enabling stress transfer; this contributes greatly to the enhancement of the monolithic
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behavior of the structural parts. Grout injection is considered a practical and effective
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repair technique that can be used without altering the architectural aesthetics of
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historic constructions (Schuller et al., 1994). In fact, the injection of lime- and
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cement-based binary and ternary grouts have been shown to be highly effective in
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strengthening unreinforced stone and brick masonry structures (Valluzzi et al., 2001;
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Adami & Vintzileou, 2008; Vintzileou & Miltiadou-Fezans, 2008; Kalagri et al.,
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2010; Oliveira et al., 2012; Papayianni & Pachta, 2015; Vintzileou et al., 2015).
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It is worth noting that different commercial grouts might exhibit variable
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properties (Luso & Lourenço, 2016). The suitability of a repair grout depends on
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whether the fresh mix possesses adequate fluidity and stability against sedimentation.
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It also relies on the strength, stiffness, bond, chemical stability and microstructure of
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the hardened mix. Although the grouts developed for conventional masonry present
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good rheological properties, in many cases their physico-mechanical properties render
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them inappropriate for the repair of adobe structures. Many lime- and cement-based
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grouts are substantially stronger and stiffer than adobe bricks and bedding earth
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mortars. Hence they are unable to follow the levels of deformation of the adobe
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masonry generated by recurrent static, seismic and thermal loads; this may cause
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undesirable damage (Silva et al., 2009). Moreover, due to the comparatively low
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porosity of some of the aforementioned grouts, they tend to act as moisture barriers
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affecting water vapor transport (Silva et al., 2014). Finally, cementitious grouts can
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introduce sulfates and other salts that may enhance the decay of adobe masonry.
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Therefore, efforts are currently in progress for the design of grout mixtures
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compatible with earthen materials.
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The use of adobe’s basic constituent material (i.e. unfired earth) in the
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composition of repair grouts seems to be an obvious solution to ensure compatibility.
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Hence, emphasis has been given on the development of either unmodified or modified
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mud grouts. Unmodified mud grouts are suspensions constituting of earth and other
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aggregates, whose hardening relies solely on the drying of the clay fraction, whereas
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modified mud grouts contain additional binders such as cement, lime and gypsum.
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An example of a design methodology for a mud grout and of its practical
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implementation in repair works with injection can be found in Roselund (1990). The
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design methodology presented in the aforementioned study considered both
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unmodified and modified mud grouts incorporating varying amounts of Portland
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cement and/or fly ash and lime. Evaluation tests showed that: (a) unmodified mud
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grouts tend to suffer from excessive shrinkage, (b) the addition of Portland cement
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may result in grouts significantly harder and stronger than adobe and (c) the use of
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lime and fly ash can improve the fresh and hardened properties of the mud grout.
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Based on these observations, a mud grout was designed for the restoration of the Pio
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Pico mansion in California, the composition of which consisted of a mixture of silty
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sand soil, silica sand, fly ash and lime. A survey undertaken by Tolles et al. (1996),
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after the 1994 Northridge Earthquake, revealed that the injection repair implemented
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at Pio Pico during 1991 succeeded in limiting crack re-opening and prevented
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excessive damage propagation during the earthquake.
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Injection of mud grouts was also used in the reconstruction of the Sistani House
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that collapsed during the 2003 Iran Bam Earthquake. Extensive laboratory testing was
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conducted at Dresden University of Technology, in order to define injectable mixtures
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that would be compatible with the monument’s building materials (Jäger & Fuchs,
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2008). Within this framework, the properties of mud grouts modified by the addition
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of cement, lime and water-reducing agents such as potassic and sodium water glass
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were assessed through compression, bending and splitting tests. The experimental
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program led to the development of a mix design incorporating clay powder, lime and
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natural wallpaper paste.
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Research aiming at evaluating the performance of grouts composed of
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unamended lean clay soil and of mud slurries stabilized with cement, lime and
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gypsum was undertaken at the Pontifical Catholic University of Peru (Vargas et al.,
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2008). For this purpose, splitting tests were carried out on adobe couplets bonded by a
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layer of grout. In addition, diagonal compression tests were performed on cracked
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adobe masonry wallets that were repaired by means of grout injection. The results of
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the aforementioned tests showed that unmodified mud grouts generally exhibit better
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adhesion capacity and also have the potential to fully restore the shear strength of
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cracked adobe masonry. The repair efficiency of the injection of an unmodified mud
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grout was further investigated through shake table tests on a full-scale model of an
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adobe house. By comparing the dynamic response of the model structure before and
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after repair with injection, Blondet et al. (2012) concluded that, at the global building
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scale, the injection of mud grouts can only achieve partial recovery of the overall
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stiffness and load-bearing capacity. Subsequent shaking tests showed that adequate
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seismic strengthening of damaged adobe buildings can be achieved by combining the
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injection of mud grouts with the installation of a nylon rope grid, confining the whole
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masonry structure (Blondet et al., 2014).
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Significant experimental work regarding the development, characterization and
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validation of mud grouts for the repair of earthen constructions has been carried out
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during a collaboration research between the University of Leuven, Belgium, and the
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University of Minho, Portugal. An extended parametric study involving the
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production and testing of 98 mixtures containing kaolin clay, limestone powder and
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sodium hexametaphosphate (HMP) at different proportions was undertaken to
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examine the effect of the composition of unmodified mud grouts on their rheology at
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fresh state and strength at hardened state (Silva et al., 2010; Silva et al., 2012). Results
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obtained from Marsh cone and rheometer tests revealed that fluidity depends on the
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colloidal behavior of the clay fraction and can be improved by the addition of
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deflocculants/dispersants for clay, such as HMP. Moreover, it was observed that
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mixtures containing larger amounts of clay develop higher flexural and compressive
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strengths. In order to evaluate the repair effectiveness, rammed earth specimens that
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had failed under bending and diagonal compression were injected with mud grouts
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composed of different soil types and were then re-tested (Silva, 2013; Silva et al.,
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2016). The experimental outcome showed that incorporating the soil composing the
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rammed earth in the mix design of the repair grout can promote higher strength
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recovery rates. Nevertheless, although the tested specimens regained a satisfactory
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amount of their original strength, the initial shear stiffness could not be restored.
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Other researchers considered the use of lime-based instead of mud-based grouts.
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Figueiredo et al. (2013) performed cyclic horizontal loading tests on a cracked full-
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scale adobe wall, which was injected with hydraulic lime slurry and wrapped with a
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synthetic mesh embedded in a lime mortar coating. The adopted retrofitting solution
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increased the ductility and shear capacity of the wall; however, definite conclusions
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on the contribution of the injection repair per se could not be drawn. Müller et al.
212
(2016) designed a grouting material composed of hydrated lime, pozzolanas (silica
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fume and fly ash) and fine aggregates (limestone powder and kaolin). This grout
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formulation was tested on cob wallets subjected to diagonal compression tests. The
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aforementioned researchers concluded that lime-based grouts fail to provide adequate
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strength recovery and hence recommended combining injection repair with additional
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strengthening solutions (Muller et al., 2016).
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Based on information available in the literature, the repair of cracks with grout
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injection apparently performs better for adobe masonry structures than for monolithic
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earthen structures, such as rammed earth and cob. Furthermore, it can be assumed that
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unmodified mud grouts are potentially more suitable for the repair of adobe
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structures. However, further research is required to reliably validate their repair
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effectiveness. Most studies evaluate efficiency based on the grout mixtures’ properties
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or on the strength recovery rate achieved by injecting individual masonry specimens.
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It is thus difficult to predict the effect of grouting on the global structural behavior of
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full buildings. The present study aims to contribute to this field by examining the
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response of an adobe model building repaired with an unmodified mud grout and
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tested under lateral static loading.
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3. Testing of the model building before repair
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Aiming at investigating the behavior of adobe buildings under lateral loading
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and at calibrating valid numerical models for the simulation of their structural
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response, a 1:2 scaled replica of a vernacular Cypriot dwelling was constructed and
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tested at the Structures Laboratory of the University of Cyprus (Illampas et al.,
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2014a). The model structure was built using scaled-down adobes with dimensions
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(height x length x width) 3 x 22 x 15 cm3. The adobes were supplied by a local
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producer and were laid using earth mortar prepared in the laboratory. The masonry
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units and bedding mortar had similar composition. For their production, soil and straw
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fibers (3-25 mm in length; 20-40% v/v) were mechanically mixed with water. Adobe
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bricks were shaped by mold casting and were allowed to dry outdoors, on a flat
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concrete surface. The soil used for producing the adobes and bedding mortar was a
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local fine-grained lean clay (ASTM D2487) with a maximum particle size of 0.6 mm.
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The properties of the soil are given in Table 1, while its particle size distribution is
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shown in Fig. 2. The mechanical properties of the adobe bricks and earth mortar are
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reported in Table 2. Masonry construction followed a running bond pattern, while the
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mortar joints’ thickness was kept <10 mm.
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Table 1. Granulometry (ASTM D422), Atterberg limits (BS 1377-2) and specific gravity (ASTM
247
D854) of the soil used in the production of the adobe bricks and bedding earth mortar composing the
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model structure under study.
Granulometry
Atterberg limits*
Specific
Sand (%)
Silt (%)
Clay (%)
LL
PL
PI
gravity of
(75 μm < d ≤ 2.36 mm)
(2 μm < d ≤ 75 μm)
(d < 2 μm)
(%)
(%)
(%)
soil solids
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63
28
41
25
16
2.85
*LL = Liquid Limit, PL = Plastic Limit, PI = Plasticity Index.
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250
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Figure 2. Particle size distribution of the soil composing the adobe bricks and bedding earth mortar
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used in the construction of the tested model building. The continuous red line shows the d < 0.18 mm
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fraction of the soil used in the preparation of the mud grout examined in this study.
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Table 2. Average properties (coefficient of variation) of the materials used in the construction of the
255
adobe model building.
Masonry constituent
Apparent density
Compressive strength
Bending strength
(kg/m3)
(MPa)
(MPa)
Adobe brick*
1300
1.28 (22%)
0.43 (18%)
Earth mortar**
1280
1.86 (12%)
1.08 (16%)
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*Results correspond to compression tests on 30 cylinders extracted from adobes (Illampas et al. 2014b)
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and three-point bending tests on 12 half-brick specimens.
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**Results correspond to standardized compression and bending tests (EN 1015-11) on 19 mortar
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sample prisms.
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The geometry of the model building and the respective test setup are illustrated
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in Fig. 3. The walls measured 220 mm in thickness and composed a rectangular
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structure with external plan dimensions (width x length) 1.75 x 3.60 m2. The
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longitudinal façade wall was 1.50 m high. The opposite rear wall was raised further
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by 0.15 m (total height = 1.65 m) to allow for the construction of a single-pitched
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roof. The roof consisted of parallel timber rafters (45 x 90 mm2 in cross-section) set
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into the masonry at 0.40 m intervals with the application of gypsum mortar. To
267
account for the weight of roof covering, adobe bricks were uniformly placed upon a
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20 mm-thick wooden panel that was nailed onto the rafters. At the center of the
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façade, a door opening (1.10 m high and 0.70 m wide) was formed. The two sidewalls
270
incorporated square window openings measuring 0.55 m in width. The load-bearing
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header of all openings comprised of timber elements 85 x 85 mm2 in cross-section
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that were installed using gypsum mortar.
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(a)
(b)
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Figure 3. Axonometric projections of the experimental set-up: (a) façade; (b) rear and side walls.
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Points 1-17 correspond to positions where displacements were measured by LVDTs. During the initial
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loading cycles, monitoring points 1-15 were used, whereas for the tests conducted after the mud grout
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injection repairs, LVDTs originally positioned at points 5 and 6 were moved to points 16 and 17. The
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displacement curves presented in this paper refer to monitoring points 1 and 3 at the façade wall, and
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13 at the rear wall.
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Testing commenced 9 weeks after the completion of the construction and
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involved a series of ten lateral loading-unloading cycles, in which the imposed static
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horizontal load was increased until noticeable damage of the masonry walls was
282
observed. After the unloading phases, the model was inspected visually, the
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permanent deformation was measured and a new test cycle was initiated. During each
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cycle, the force-displacement response of the masonry walls was monitored and the
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cracking damage induced was recorded.
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The load in each cycle was applied monotonically along the length of the rear
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wall, at approximately 2/3 of the structure’s height. The load-imposition system
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consisted of a timber beam attached on the swivel head of a 60 kN-capacity hydraulic
289
jack. Linear Variable Differential Transducers (LVDTs) (range ± 50.8 mm, accuracy
290
± 0.25%) were used for measuring the deformations occurring in the model during the
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tests. Fig. 3 presents the position of the points (1-15) monitored during the test;
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displacements in the horizontal direction vertical to the load were measured at points
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10-12, whilst displacements in the load direction were measured at all other points.
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The displacement curves presented in this paper refer to two monitoring points at the
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façade wall, and one at the rear wall, which are considered representative. Crack
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opening-closing was monitored with digital cameras.
297
The outcome of the initial tests conducted is presented in Figs. 4 and 5, in terms
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of damage pattern and envelope force-displacement curves recorded at the side, rear
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and façade walls. The experimental data obtained indicate that damage evolution
300
under lateral loading is significantly affected by the lack of diaphragmatic function at
301
the roof level, which precludes integral box action and leads to stress localization. As
302
a result, cracking in the model structure was concentrated at the rear and the two
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sidewalls, while the façade wall and the timber elements remained practically intact.
15
(a)
(b)
(c)
(d)
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Figure 4. Cracking damage recorded after the initial test at the two sidewalls (a), the interior of the rear
305
wall’s upper central section (b), and at the lower (c) and upper (d) parts of the rear wall’s exterior
306
surface.
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307
308
Figure 5. Force-displacement envelopes of the initial test, obtained from the data recorded at the rear
309
(LVDT 13), façade (LVDT 1) and sidewalls (LVDT 3) of the model.
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Damage at the two sidewalls was characterized by diagonal shear cracking
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radiating from the corners of the window openings (Fig. 4a). Bulging at the load
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imposition point led to the development of horizontal and diagonal cracks at the
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interior of the rear wall (Fig. 4b). Out-of-plane bending caused continuous horizontal
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cracking at the base region of the rear wall’s exterior surface (Fig. 4c). In addition,
315
failure of the bonding gypsum mortar at the roof’s supports and subsequent sliding of
316
the timber rafters was noted (Fig. 4d). In all cases, crack initiation and propagation
317
was caused by loss of cohesion at the brick-mortar interfaces, rather than failure of the
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masonry materials themselves. The opening size of the cracks ranged from 5 to
319
20 mm.
320
The force-displacement behavior (Fig. 5) is highly nonlinear and indicates that
321
interaction among the structure’s load-bearing elements is effectively lost at relatively
322
low levels of deformation. Up to a lateral translation of about 2 mm, the masonry
323
walls exhibited consistent structural response and a uniform distribution of the
324
deformations induced was noted. When the imposed load exceeded 10.6 kN, stiffness
325
degradation and cracking damage started to develop. At levels of loading above
326
12 kN, homogeneous response of the structural system ceased to exist and differential
327
movement of the masonry walls took place. The maximum lateral load capacity
328
recorded was 14.2 kN and accounts for approximately 30% of the model building’s
329
self-weight. After the load-bearing capacity was exceeded, damage propagation
330
gradually led to splitting of the two sidewalls due to diagonal shear cracking. As a
331
result, a kinematic rocking mechanism was formed and the overall load capacity fell
332
to a residual value of 9.1 kN. The ultimate out-of-plane translation measured at the
333
rear wall’s upper central section was 96 mm, which corresponds to a drift (=
334
horizontal displacement/monitoring point’s vertical distance from the building’s base)
335
of 6.4%. The displacements generated at the upper part of the side and façade walls
336
were significantly lower, reaching a maximum value of 26 mm, which accounts for a
337
drift of 1.7%.
338
4. Repair of the damaged model building
339
Following the initial test described in the previous section, the adobe model
340
building was repaired by means of mud grout injection. The design of the mud grout
341
used was based on previous experimental research carried out by Silva (2013). It was
18
342
decided to use an unmodified mud grout containing the same lean clay soil used in the
343
production of the adobe bricks and bedding mortar composing the model building (see
344
Table 1 and Fig. 2). The soil was subjected to dry sieving in order to remove particles
345
with grain sizes d ≥ 0.18 mm. Limestone powder (d < 0.025 mm) was also
346
incorporated into the mixture to decrease the clay content, while increasing the
347
volumetric solid fraction, thus limiting excessive drying shrinkage (Silva et al., 2012).
348
Furthermore, HMP clay deflocculant was used to reduce the water-to-solids ratio
349
(w/s) and to improve the fluidity of the grout. The solid constituents of the mixture
350
consisted of 30% soil and 70% limestone powder. Approximately 5 g of deflocculant
351
(HMP) were added for every 1 kg of solid constituents, while a w/s ratio of about 0.45
352
was used. These values were defined following trials with the Marsh funnel test
353
according to ASTM D6910. It should be noted that complete flow is achieved for a
354
grout of approximately null yield stress, which is a requirement for good injectability
355
properties. The value of w/s ratio used for the grout adopted in this study is larger
356
than those used by Silva et al. (2012). This difference is probably a consequence of
357
the different clay fractions contained in each grout, in terms of content percentage,
358
particle size distribution below micro-size and clay mineralogy.
359
For the preparation of the grout, the soil and limestone powder were initially
360
mixed manually and the HMP was dissolved in tap water. The blend of solid phase
361
materials was then progressively added into the solution containing the deflocculant
362
and was kneaded to form a suspension. The latter was mixed using a manually
363
controlled 1200 rpm power drill equipped with a twin propeller mixing paddle, until a
364
homogenous mud grout was obtained. In order to produce sufficient amount of grout
365
for the execution of the injection repair, the aforementioned mixing procedure was
19
366
repeated 4 times and the respective flow time through the Marsh funnel was assessed
367
(ASTM D6910).
368
Furthermore, three beam specimens measuring 40 x 40 x 160 mm3 were mold
369
casted from each of the four mixtures in accordance with EN 1015-11. The beam
370
specimens were removed from the molds 5 days after casting and were allowed to dry
371
indoors in the laboratory (30 ± 2 oC and 45 ± 7% R.H.) for another 37 days. At the
372
end of the 42-days, which coincided with the time of testing the model building, the
373
weight and dimensions of the specimens were measured. Volumetric shrinkage was
374
estimated based on the original size of the molds and the final dimensions of the
375
specimens. The apparent density of the material was also evaluated using the
376
gravimetric measurements conducted. The hardened beam specimens were then
377
subjected to three-point bending tests. The two half-specimens obtained after the
378
flexural failure of each test unit were further subjected to compression tests using the
379
jig described in EN 1015-11. It is worth noting that, in some cases, the hardened grout
380
suffered from shrinkage cracks. As a result, only 9 out of the 12 beam specimens
381
sampled could be used in bending tests.
382
The outcome of the experiments conducted for the characterization of the mud
383
grout is summarized in Table 3. The average flow time of the fresh mixtures was 104
384
s at T = 28 oC. This is below the 200-700 s corresponding values reported by Silva et
385
al. (2012) for mud grouts containing kaolin clay, limestone powder and HMP. It can
386
thus be argued that the material hereby studied possesses adequate fluidity. However,
387
the mold casted grout specimens sustained significant volumetric shrinkage that
388
ranged from 16% to 21%. This is attributed to the rather high w/s ratio adopted in the
389
mix design for the grout. The aforementioned high volumetric shrinkage also explains
20
390
the cracking observed in certain grout specimens. The hardened material’s apparent
391
density was about 1575 kg/m3; this is lower than the 1700-1900 kg/m3 densities of the
392
mixtures examined by Silva (2013). The bending strength of the tested specimens lay
393
between 1.1 and 1.4 MPa, while the compressive strength values varied from 1.8 to
394
2.4 MPa. In general, the mud grout presented higher strength than the adobe bricks
395
and the bedding earth mortar used in the construction of the model. The consistent
396
results obtained from all tests conducted on grout samples indicate that the 4 mixtures
397
prepared had identical properties.
398
Table 3. Average properties of the mud grout from 4 batches (coefficient of variation).
Flow time (s)
104 (13%)
399
Apparent density
Volumetric
Compressive
Bending strength
(kg/m3)
shrinkage (%)
strength (MPa)
(MPa)
1575 (3%)
19 (8%)
2.21 (7%)
1.28 (6%)
To achieve an effective repair, all cracks on the structure were identified and
400
adequately injected. In practice, the paths of masonry cracks are often visually
401
detected through fissures and/or detachments of plaster. Since the walls of the model
402
building under study were not plastered, and due to the fact that complete closing of
403
certain cracks was observed upon unloading (Illampas et al., 2014a), prior to the
404
initiation of the injection works, the structure was laterally loaded until all generated
405
cracks became visible again (2 mm < crack opening < 10 mm). Although this
406
approach may seem rather unconventional, it ensured that all damaged areas could be
407
effectively detected and injected, so as to obtain comparable results regarding the
408
effectiveness of the repair method.
21
(a)
(b)
409
Figure 6. Injection repair of the model: (a) installation of the injection tubes and sealing of the cracks
410
with earth mortar; (b) injection of mud grout into a crack.
411
All crack paths were marked on the surface of the masonry with spray paint
412
(Fig. 4) and loose debris was removed from the failure planes using pressurized air.
413
Flexible plastic tubes with 5 mm diameter were then inserted every 50-100 mm along
414
the length of the cracks (Fig. 6a). The plastic tubes extended into approximately the
22
415
mid-thickness of the walls and were set in place with the application of earth mortar
416
prepared in the laboratory. The same earth mortar was also used for sealing the
417
cracks. The grout was injected into the damaged areas using a 100 mL syringe (Fig.
418
6b). The nozzle of the syringe was initially fitted into the injection tubes at the
419
bottom-end of each crack. Once the injected grout material appeared at a tube above
420
the injection point, the injected tube was sealed. Injection then continued from the
421
leaking tube upwards; the procedure was repeated until all tubes along a crack were
422
filled with grout.
423
The injection works were completed in 4 successive days. The cumulative
424
length of cracks injected was ca. 30 m. The total volume of the grout material used
425
was 24.6 L. The amount of grout injected at the exterior side of the rear wall was
426
3.6 L. This was applied to the horizontal and diagonal cracks formed at the lower and
427
upper parts of the rear wall and at the abutments of the roof rafters. Repairing damage
428
at the interior side of the rear wall required 12.1 L of grout, due to the significantly
429
larger opening of the cracks formed at this area. The two sidewalls, which exhibited
430
similar crack patterns, required approximately the same quantity of grout: 4.4 and 4.5
431
L.
432
5. Testing of the model building after repair
433
The model building was tested 42 days after the completion of the injection
434
repair. The test setup implemented for the initial test of the model, as described in
435
Section 3, was also adopted for assessing the response of the repaired model (see Fig.
436
3). However, the LVDTs originally positioned at points 5 and 6 were moved to points
437
16 and 17. The testing procedure was also similar, but the loading cycles applied to
438
the repaired model were reduced to four.
23
Rear wall - Interior
Rear wall - Exterior
Side walls - Exterior
Crack pattern recorded before repair
Crack pattern recorded after repair
439
Figure 7. Comparison between the crack pattern of the model building before and after repair.
24
440
The crack pattern observed on the masonry walls of the repaired model,
441
following the completion of the 4 loading cycles, is shown in Fig. 7. This figure also
442
compares the new crack pattern with that observed before repair, showing similar
443
development. Again, overstressing along the line of loading led to the development of
444
horizontal and diagonal cracks at the interior of the rear wall. At the exterior surface
445
of the rear wall, a major horizontal crack was noted approximately 25 cm above the
446
model’s base. This was caused by out-of-plane bending. Due to the restraints imposed
447
from the two sidewalls, the aforementioned crack followed inclined paths towards the
448
two ends of the rear wall. However, a noticeable difference was observed with respect
449
to the formation of several horizontal cracks, just below the abutments of the roof
450
rafters. This behavior seems to be a consequence of the better bonding achieved
451
between the adobe masonry and the timber elements, promoted by the injection of the
452
mud grout in this region. In-plane loading of the two sidewalls caused diagonal
453
cracking that initiated at the corners of the windows and propagated towards the upper
454
and lower sides of the walls. These cracks extended throughout the whole thickness of
455
the masonry. All major cracks were generated during the first and second loading
456
cycles. Subsequent loading during the third and fourth cycles remobilized opening of
457
pre-existing cracks and led to larger crack openings.
458
Despite the fact that the damage of the repaired model mainly occurred at the
459
same wall sections, cracks mostly did not follow exactly their original paths. Instead
460
of propagating through the injected cracks, the new cracks developed through
461
adjacent mortar joints. The observed failure mechanism was characterized by
462
debonding at the interfaces between the adobe bricks and the mortar or the grout (Fig.
463
8). Inspection of the few injected cracks that re-opened revealed that these were
464
adequately filled with the grout material used; failure of the latter was not observed.
25
465
More importantly, damage mitigation to the masonry constituents was also not
466
observed, although the bending and compressive strengths of the grout were higher
467
than the equivalent properties of the adobe bricks and bedding mortar. Crack opening
468
during all loading cycles was significant, with sizes varying from 4 to 25 mm (see
469
Fig. 8).
470
471
Figure 8. Characteristic crack opening and mode of failure recorded at the central section of the rear
472
wall’s interior surface.
473
The forces imposed during the implementation of each loading-unloading cycle
474
and the corresponding cumulative displacements recorded at the model building’s
475
rear, façade and sidewalls are presented in Fig. 9, along with the force-displacement
476
envelopes obtained from the measurements conducted at the same monitoring points
477
during the initial test. Cumulative lateral translations were computed by adding to the
478
displacements measured at each individual loading cycle the permanent deformations
479
measured after the completion of each cycle.
26
(a)
(b)
(c)
480
Figure 9. Comparison between the force-displacement data recorded at (a) the rear (LVDT 13), (b) the
481
façade (LVDT 1) and (c) the side (LVDT 3) walls after the injection repairs (continuous lines) and the
482
data envelopes obtained from the initial load testing of the original model building (dashed lines). The
483
characteristic data points (▲, ●, ■), which have been used to form the force–displacement
484
envelopes, are noted in the diagrams.
27
485
The maximum lateral load capacity of the repaired model was 13.2 kN, which
486
exceeds by almost 45% the residual capacity recorded after the formation of the
487
kinematic mechanism observed in the first test, as a result of extensive cracking.
488
Furthermore, the grout injection repair reinstated more than 90% of the initial lateral
489
load capacity. Stiffness degradation of the repaired model initiated at 5.3 kN, while in
490
the initial test the model behaved linearly to loading up to 10.6 kN. However, a rather
491
homogenous distribution of the displacements measured at the various sections of the
492
repaired building was noted up to a lateral translation of 9 mm and an imposed force
493
of 12 kN. Furthermore, the stiffness of the rear and sidewalls was fully recovered after
494
the repair of the model. Interestingly enough, the out-of-plane stiffness estimated
495
from the force-displacement response of the façade wall increased and became equal
496
to that of the rear wall. This behavior indicates that the grout injected at the abutments
497
of the timber roof beams significantly improved the connection between the masonry
498
and the roof. Hence, during the first loading cycle, the roof was able to effectively
499
distribute the loads to all parts of the structure and the walls could therefore function
500
as members of a consistent structural system. Soon after horizontal cracking
501
developed at the vicinity of the roof supports, integral box effect was lost and
502
differential movement of the load-bearing elements was noted.
503
During the second cycle, damage propagation at the rear wall was quite rapid.
504
As a result, significantly greater deformations were generated at this section,
505
particularly at the load-imposition region, where the stresses exerted were much
506
higher. When the applied load attained its maximum value, the out-of-plane
507
displacement of the rear wall reached 55 mm, while the horizontal translation
508
measured at the side and façade walls was close to 20 mm. Although a reduction in
509
the load-bearing capacity of the repaired model was recorded at the third and fourth
28
510
loading cycles, an abrupt drop in the overall lateral capacity was not noted at the
511
levels of deformation monitored. The residual capacity at the end of the experimental
512
procedure was 11.6 kN. The ultimate displacements recorded at the upper sections of
513
the rear, façade and sidewalls were 83, 32 and 28 mm, respectively. In terms of lateral
514
drift, these values can be interpreted as 5.7%, 2.1% and 1.8%.
515
Diagonal compression (shear) static tests carried out on various types of earth
516
masonry indicate that the repair of cracks with mud grout injection can restore a
517
significant portion of the initial in-plane load-bearing capacity (Vargas et al., 2008;
518
Silva, 2013). Under monotonic horizontal loading, the overall lateral strength of the
519
model building primarily depends on the response of the in-plane resisting elements.
520
Therefore, the effectiveness of the repairs hereby examined is mainly attributed to the
521
injection repair carried out at the cracks formed on the two sidewalls. The higher than
522
90% strength recovery achieved well exceeds the 54% corresponding value reported
523
by Blondet et al. (2012), who performed shake table (rather than static) tests on an
524
adobe model house also repaired with the injection of an unmodified mud grout. The
525
same researchers reported a 30% stiffness recovery rate after the repair, whereas the
526
grout hereby used in static tests succeeded in fully re-establishing the initial stiffness
527
of the adobe masonry walls.
528
6. Conclusions
529
In this study, the effectiveness of the injection of unmodified mud grouts to
530
repair cracks in adobe masonry walls was assessed. For this purpose, static lateral
531
loading laboratory tests were undertaken on a 1:2 scaled adobe model building. The
532
cracks previously formed on the model’s walls were injected with an unmodified mud
533
grout containing the same soil used in the fabrication of the masonry constituents.
29
534
The grout mixture hereby examined exhibited adequate fluidity and sufficient
535
mechanical strength. However, its introduction into the cracks entailed certain
536
difficulties associated with the closing of the cracks upon unloading. This implies
537
that, in practice, it would be essential to inspect thoroughly all areas of the masonry to
538
identify all existing cracks and then open these up, using for example mechanical
539
means (e.g. drills), before performing the injection repair. Nevertheless, this is
540
normally not so difficult, as walls are plastered and cracks can be easily observed.
541
The results obtained from the loading tests indicate that the injection of mud
542
grouts can improve the structural performance of damaged adobe buildings by
543
reinstating the monolithic behavior of cracked sections and/or by enhancing the bond
544
between the load-bearing elements. This can lead to significant recovery of the
545
building’s initial stiffness and lateral strength. The recorded modes of failure show
546
that the efficiency of the injection repair relies heavily on the cohesive strength
547
developed between the grout material and the masonry components. Furthermore, it
548
was observed that grouting can strengthen the connection between the walls and the
549
roof structure when it is applied to the areas where timber beams are set into the
550
masonry. However, at increased levels of loading, the bonding introduced between
551
these elements is still unable to compensate for the lack of diaphragmatic function,
552
which requires additional measures (e.g. installation of ring beams, reinforcing
553
anchors, transversal ties, etc.).
554
Based on the outcomes of the research conducted, it can be argued that the
555
repair of cracks with mud grout injection is useful for re-establishing the structural
556
stability of adobe constructions under horizontal loads.
557
30
558
Acknowledgements
559
This study was partly financed by FEDER funds through the Competitivity Factors
560
Operational Programme – COMPETE, and by national funds through FCT –
561
Foundation for Science and Technology, within the scope of the projects POCI-01-
562
0145-FEDER-007633 and POCI-01-0145-FEDER-016737 (PTDC/ECM-
563
EST/2777/2014). The support from grant SFRH/BPD/97082/2013 is also
564
acknowledged.
565
566
Conflict of interest
567
The authors declare that they have no conflict of interest.
568
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