Elsevier Editorial System(tm) for Construction & Building Materials Manuscript Draft Manuscript Number: 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 1 Validation of the repair effectiveness of mud 2 grout injections by lateral load testing of an 3 adobe model building 4 Rogiros Illampas1, Rui A. Silva2, Dimos C. Charmpis1, Paulo B. Lourenço2, Ioannis 5 Ioannou1* 6 1 7 Kallipoleos str., P.O. Box 20537, 1678 Nicosia, Cyprus 8 Phone: +357 22892257 9 Fax: +357 22895318 10 Emails: rilamp01@ucy.ac.cy; charmpis@ucy.ac.cy; ioannis@ucy.ac.cy * 11 URL: http://www.ucy.ac.cy/cee/en/ Department of Civil and Environmental Engineering, University of Cyprus, 75, 12 13 2 14 4800-058 Guimarães, Portugal 15 Phone: +351 253510200 16 Fax: +351 253510217 17 Emails: ruisilva@civil.uminho.pt; pbl@civil.uminho.pt 18 URL: http://www.isise.net/ Department of Civil Engineering, ISISE, University of Minho, Campus de Azurém 19 20 *Corresponding author 21 22 23 1 24 Abstract 25 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 30 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 37 Adobe masonry, grouting repair, mud grout, horizontal loading, static tests 38 39 40 41 42 43 44 45 46 47 48 49 2 50 51 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, 60 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 68 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) 76 Figure 1. Cracks on adobe masonry walls in the mountainous village of Kakopetria (a) and in the 77 coastal city of Limassol (b) in Cyprus. 4 78 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. 88 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 91 raised regarding the effectiveness of these techniques because certain interventions 92 fail to reinstate monolithic behavior of the element, while others are considered 93 excessively intrusive and costly as they involve considerable loss of fabric. 94 Furthermore, installing materials much stiffer than adobe (e.g. steel or concrete) into 95 cracked sections can result in adverse effects, since such interventions cause abnormal 96 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, 98 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 101 injection of mud grouts on the recovery of the load-bearing and deformation capacity 5 102 of damaged adobe masonry constructions. For this purpose, a 1:2 scaled model of an 103 existing adobe building from Cyprus was constructed and tested at the laboratory 104 under monotonic static lateral loading. After subjecting the model building to a 105 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 107 grout and a new series of tests was undertaken. The structural behavior of the model 108 before and after repair is hereby compared in terms of the recorded force- 109 displacement response, damage distribution and failure mode. It is worth noting that 110 this is one of the few studies that assess the effectiveness of mud grout injection 111 through laboratory tests on a large scale specimen, namely a full model of an adobe 112 building. 113 2. Repair of earth constructions with grout injection 114 Grouts are essentially fluid mortar mixtures that can be injected into cracks, 115 fissures or gaps using gravity flow or pressure-assisted pumping. As the grout fills 116 these voids and hardens, it provides adhesion between the masonry materials, re- 117 enabling stress transfer; this contributes greatly to the enhancement of the monolithic 118 behavior of the structural parts. Grout injection is considered a practical and effective 119 repair technique that can be used without altering the architectural aesthetics of 120 historic constructions (Schuller et al., 1994). In fact, the injection of lime- and 121 cement-based binary and ternary grouts have been shown to be highly effective in 122 strengthening unreinforced stone and brick masonry structures (Valluzzi et al., 2001; 123 Adami & Vintzileou, 2008; Vintzileou & Miltiadou-Fezans, 2008; Kalagri et al., 124 2010; Oliveira et al., 2012; Papayianni & Pachta, 2015; Vintzileou et al., 2015). 6 125 It is worth noting that different commercial grouts might exhibit variable 126 properties (Luso & Lourenço, 2016). The suitability of a repair grout depends on 127 whether the fresh mix possesses adequate fluidity and stability against sedimentation. 128 It also relies on the strength, stiffness, bond, chemical stability and microstructure of 129 the hardened mix. Although the grouts developed for conventional masonry present 130 good rheological properties, in many cases their physico-mechanical properties render 131 them inappropriate for the repair of adobe structures. Many lime- and cement-based 132 grouts are substantially stronger and stiffer than adobe bricks and bedding earth 133 mortars. Hence they are unable to follow the levels of deformation of the adobe 134 masonry generated by recurrent static, seismic and thermal loads; this may cause 135 undesirable damage (Silva et al., 2009). Moreover, due to the comparatively low 136 porosity of some of the aforementioned grouts, they tend to act as moisture barriers 137 affecting water vapor transport (Silva et al., 2014). Finally, cementitious grouts can 138 introduce sulfates and other salts that may enhance the decay of adobe masonry. 139 Therefore, efforts are currently in progress for the design of grout mixtures 140 compatible with earthen materials. 141 The use of adobe’s basic constituent material (i.e. unfired earth) in the 142 composition of repair grouts seems to be an obvious solution to ensure compatibility. 143 Hence, emphasis has been given on the development of either unmodified or modified 144 mud grouts. Unmodified mud grouts are suspensions constituting of earth and other 145 aggregates, whose hardening relies solely on the drying of the clay fraction, whereas 146 modified mud grouts contain additional binders such as cement, lime and gypsum. 147 An example of a design methodology for a mud grout and of its practical 148 implementation in repair works with injection can be found in Roselund (1990). The 7 149 design methodology presented in the aforementioned study considered both 150 unmodified and modified mud grouts incorporating varying amounts of Portland 151 cement and/or fly ash and lime. Evaluation tests showed that: (a) unmodified mud 152 grouts tend to suffer from excessive shrinkage, (b) the addition of Portland cement 153 may result in grouts significantly harder and stronger than adobe and (c) the use of 154 lime and fly ash can improve the fresh and hardened properties of the mud grout. 155 Based on these observations, a mud grout was designed for the restoration of the Pio 156 Pico mansion in California, the composition of which consisted of a mixture of silty 157 sand soil, silica sand, fly ash and lime. A survey undertaken by Tolles et al. (1996), 158 after the 1994 Northridge Earthquake, revealed that the injection repair implemented 159 at Pio Pico during 1991 succeeded in limiting crack re-opening and prevented 160 excessive damage propagation during the earthquake. 161 Injection of mud grouts was also used in the reconstruction of the Sistani House 162 that collapsed during the 2003 Iran Bam Earthquake. Extensive laboratory testing was 163 conducted at Dresden University of Technology, in order to define injectable mixtures 164 that would be compatible with the monument’s building materials (Jäger & Fuchs, 165 2008). Within this framework, the properties of mud grouts modified by the addition 166 of cement, lime and water-reducing agents such as potassic and sodium water glass 167 were assessed through compression, bending and splitting tests. The experimental 168 program led to the development of a mix design incorporating clay powder, lime and 169 natural wallpaper paste. 170 Research aiming at evaluating the performance of grouts composed of 171 unamended lean clay soil and of mud slurries stabilized with cement, lime and 172 gypsum was undertaken at the Pontifical Catholic University of Peru (Vargas et al., 8 173 2008). For this purpose, splitting tests were carried out on adobe couplets bonded by a 174 layer of grout. In addition, diagonal compression tests were performed on cracked 175 adobe masonry wallets that were repaired by means of grout injection. The results of 176 the aforementioned tests showed that unmodified mud grouts generally exhibit better 177 adhesion capacity and also have the potential to fully restore the shear strength of 178 cracked adobe masonry. The repair efficiency of the injection of an unmodified mud 179 grout was further investigated through shake table tests on a full-scale model of an 180 adobe house. By comparing the dynamic response of the model structure before and 181 after repair with injection, Blondet et al. (2012) concluded that, at the global building 182 scale, the injection of mud grouts can only achieve partial recovery of the overall 183 stiffness and load-bearing capacity. Subsequent shaking tests showed that adequate 184 seismic strengthening of damaged adobe buildings can be achieved by combining the 185 injection of mud grouts with the installation of a nylon rope grid, confining the whole 186 masonry structure (Blondet et al., 2014). 187 Significant experimental work regarding the development, characterization and 188 validation of mud grouts for the repair of earthen constructions has been carried out 189 during a collaboration research between the University of Leuven, Belgium, and the 190 University of Minho, Portugal. An extended parametric study involving the 191 production and testing of 98 mixtures containing kaolin clay, limestone powder and 192 sodium hexametaphosphate (HMP) at different proportions was undertaken to 193 examine the effect of the composition of unmodified mud grouts on their rheology at 194 fresh state and strength at hardened state (Silva et al., 2010; Silva et al., 2012). Results 195 obtained from Marsh cone and rheometer tests revealed that fluidity depends on the 196 colloidal behavior of the clay fraction and can be improved by the addition of 197 deflocculants/dispersants for clay, such as HMP. Moreover, it was observed that 9 198 mixtures containing larger amounts of clay develop higher flexural and compressive 199 strengths. In order to evaluate the repair effectiveness, rammed earth specimens that 200 had failed under bending and diagonal compression were injected with mud grouts 201 composed of different soil types and were then re-tested (Silva, 2013; Silva et al., 202 2016). The experimental outcome showed that incorporating the soil composing the 203 rammed earth in the mix design of the repair grout can promote higher strength 204 recovery rates. Nevertheless, although the tested specimens regained a satisfactory 205 amount of their original strength, the initial shear stiffness could not be restored. 206 Other researchers considered the use of lime-based instead of mud-based grouts. 207 Figueiredo et al. (2013) performed cyclic horizontal loading tests on a cracked full- 208 scale adobe wall, which was injected with hydraulic lime slurry and wrapped with a 209 synthetic mesh embedded in a lime mortar coating. The adopted retrofitting solution 210 increased the ductility and shear capacity of the wall; however, definite conclusions 211 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 213 fume and fly ash) and fine aggregates (limestone powder and kaolin). This grout 214 formulation was tested on cob wallets subjected to diagonal compression tests. The 215 aforementioned researchers concluded that lime-based grouts fail to provide adequate 216 strength recovery and hence recommended combining injection repair with additional 217 strengthening solutions (Muller et al., 2016). 218 Based on information available in the literature, the repair of cracks with grout 219 injection apparently performs better for adobe masonry structures than for monolithic 220 earthen structures, such as rammed earth and cob. Furthermore, it can be assumed that 221 unmodified mud grouts are potentially more suitable for the repair of adobe 10 222 structures. However, further research is required to reliably validate their repair 223 effectiveness. Most studies evaluate efficiency based on the grout mixtures’ properties 224 or on the strength recovery rate achieved by injecting individual masonry specimens. 225 It is thus difficult to predict the effect of grouting on the global structural behavior of 226 full buildings. The present study aims to contribute to this field by examining the 227 response of an adobe model building repaired with an unmodified mud grout and 228 tested under lateral static loading. 229 3. Testing of the model building before repair 230 Aiming at investigating the behavior of adobe buildings under lateral loading 231 and at calibrating valid numerical models for the simulation of their structural 232 response, a 1:2 scaled replica of a vernacular Cypriot dwelling was constructed and 233 tested at the Structures Laboratory of the University of Cyprus (Illampas et al., 234 2014a). The model structure was built using scaled-down adobes with dimensions 235 (height x length x width) 3 x 22 x 15 cm3. The adobes were supplied by a local 236 producer and were laid using earth mortar prepared in the laboratory. The masonry 237 units and bedding mortar had similar composition. For their production, soil and straw 238 fibers (3-25 mm in length; 20-40% v/v) were mechanically mixed with water. Adobe 239 bricks were shaped by mold casting and were allowed to dry outdoors, on a flat 240 concrete surface. The soil used for producing the adobes and bedding mortar was a 241 local fine-grained lean clay (ASTM D2487) with a maximum particle size of 0.6 mm. 242 The properties of the soil are given in Table 1, while its particle size distribution is 243 shown in Fig. 2. The mechanical properties of the adobe bricks and earth mortar are 244 reported in Table 2. Masonry construction followed a running bond pattern, while the 245 mortar joints’ thickness was kept <10 mm. 11 246 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 248 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 9 63 28 41 25 16 2.85 *LL = Liquid Limit, PL = Plastic Limit, PI = Plasticity Index. 249 250 251 Figure 2. Particle size distribution of the soil composing the adobe bricks and bedding earth mortar 252 used in the construction of the tested model building. The continuous red line shows the d < 0.18 mm 253 fraction of the soil used in the preparation of the mud grout examined in this study. 12 254 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%) 256 *Results correspond to compression tests on 30 cylinders extracted from adobes (Illampas et al. 2014b) 257 and three-point bending tests on 12 half-brick specimens. 258 **Results correspond to standardized compression and bending tests (EN 1015-11) on 19 mortar 259 sample prisms. 260 The geometry of the model building and the respective test setup are illustrated 261 in Fig. 3. The walls measured 220 mm in thickness and composed a rectangular 262 structure with external plan dimensions (width x length) 1.75 x 3.60 m2. The 263 longitudinal façade wall was 1.50 m high. The opposite rear wall was raised further 264 by 0.15 m (total height = 1.65 m) to allow for the construction of a single-pitched 265 roof. The roof consisted of parallel timber rafters (45 x 90 mm2 in cross-section) set 266 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 268 20 mm-thick wooden panel that was nailed onto the rafters. At the center of the 269 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 271 header of all openings comprised of timber elements 85 x 85 mm2 in cross-section 272 that were installed using gypsum mortar. 13 (a) (b) 273 Figure 3. Axonometric projections of the experimental set-up: (a) façade; (b) rear and side walls. 274 Points 1-17 correspond to positions where displacements were measured by LVDTs. During the initial 275 loading cycles, monitoring points 1-15 were used, whereas for the tests conducted after the mud grout 276 injection repairs, LVDTs originally positioned at points 5 and 6 were moved to points 16 and 17. The 277 displacement curves presented in this paper refer to monitoring points 1 and 3 at the façade wall, and 278 13 at the rear wall. 279 Testing commenced 9 weeks after the completion of the construction and 280 involved a series of ten lateral loading-unloading cycles, in which the imposed static 14 281 horizontal load was increased until noticeable damage of the masonry walls was 282 observed. After the unloading phases, the model was inspected visually, the 283 permanent deformation was measured and a new test cycle was initiated. During each 284 cycle, the force-displacement response of the masonry walls was monitored and the 285 cracking damage induced was recorded. 286 The load in each cycle was applied monotonically along the length of the rear 287 wall, at approximately 2/3 of the structure’s height. The load-imposition system 288 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 291 tests. Fig. 3 presents the position of the points (1-15) monitored during the test; 292 displacements in the horizontal direction vertical to the load were measured at points 293 10-12, whilst displacements in the load direction were measured at all other points. 294 The displacement curves presented in this paper refer to two monitoring points at the 295 façade wall, and one at the rear wall, which are considered representative. Crack 296 opening-closing was monitored with digital cameras. 297 The outcome of the initial tests conducted is presented in Figs. 4 and 5, in terms 298 of damage pattern and envelope force-displacement curves recorded at the side, rear 299 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 303 sidewalls, while the façade wall and the timber elements remained practically intact. 15 (a) (b) (c) (d) 304 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. 16 307 308 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. 310 Damage at the two sidewalls was characterized by diagonal shear cracking 311 radiating from the corners of the window openings (Fig. 4a). Bulging at the load 312 imposition point led to the development of horizontal and diagonal cracks at the 313 interior of the rear wall (Fig. 4b). Out-of-plane bending caused continuous horizontal 314 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 17 318 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 References 569 Adami, C.E. & Vintzileou, E., 2008. Interventions to historic masonries: Investigation of the bond 570 mechanism between stones or bricks and grouts. Materials and Structures, 41(2), pp.255-267. 571 ASTM D2487, 2000. Standard Practice for Classification of Soils for Engineering Purposes (Unified 572 Soil Classification System). West Conshohocken, PA: ASTM International, www.astm.org. 573 ASTM D422, 2002. Standard Test Method for Particle-Size Analysis of Soils. West Conshohocken, 574 575 576 577 578 579 PA: ASTM International, www.astm.org. ASTM D6910, 2004. Standard Test Method for Marsh Funnel Viscosity of Clay Construction Slurries. West Conshohocken, PA: ASTM International, www.astm.org. ASTM D854, 2002. Standard Test Methods for Specific Gravity of Soil Solids by Water Pycnometer. 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