1 Experimental Study of the Effect of Adding Polypropylene Fibers and PVC Waste on Cement Mortars’ Drying Shrinkage and Crack Opening Aningga, John Linard L. Journal 1 February 2, 2021 CE 8: Construction Materials and Testing with Lab Engr.Bon Ryan Aniban, Instructor 2 I. INTRODUCTION Unreinforced cement concrete is a brittle material with limited mechanical strength and properties that is susceptible to damage and deterioration brought by factors including strength failure, aging, and exposure to harsh environment conditions. Accordingly, shrinkage is a fundamental parameter developed in these concrete structures that is considered a major source of cracking and deformation. These cracks due to shrinkage are a significant cause of weakness in concrete particularly in large onsite applications leading to subsequent fracture and failure and general lack of durability (Anandan and Santhanam, 2007). It therefore, requires necessary consideration in terms of analyzing the durability of cementitious materials due to its major impact on the overall stability of the structure. Shrinkage exists in varying forms namely thermal-shrinkage, drying-shrinkage, plastic-shrinkage, and endogenous-shrinkage, these phenomenon are linked to the aging of the concrete and a result of loss of capillary water from the hardened cement mixture, leading to a decrease in relative humidity and evolution in the porous structure manifested as contraction and crack formation within the concrete. Shrinkage is a type of concrete deformation which can be measure by nondestructive method and known to be generated by parameters such as capillary pressure, relative humidity and Young’s modulus. The addition of polypropylene fiber was confirmed by numerous research studies to have improved the overall mechanical properties of concrete; increasing its compressive and flexural strength, retaining a higher internal relative humidity, 3 reducing the probability of volume reduction and subsequently delaying shrinkage and the prevention of cracks formation. This study utilizes polypropylene fiber with the addition of PVC plastic grains which is known to increase the fluidity of cementitious materials in order to delay the shrinkage phenomenon and subsequently prevent the development of cracks. The outcome of this study will also improve the existing knowledge on the phenomenon of shrinkage and predicting its effect on crack propagation. II. SYNTHESIS To analyze the effect of polypropylene fiber and PVC plastic grains in terms of parameters generating the cracking phenomenon namely internal relative humidity, Young’s modulus, and the hydration degree and porosity, an experimental study has been conducted. The experiment involved four different concrete mixtures, the first one being a reference mixture containing only limestone filler, the second has substituted PVC plastic grains to the 20% proportion of sand, the third is the replacement of 1.5% cement quantity with polypropylene fiber, and the last one is a mixture of two previous formulations having 20% of sand substituted with PVC plastic grains and 1.5% cement replaced with polypropylene fibers. The mixtures were thoroughly mixed with a specified E/L=(C+Ka) ratio of 0.5. Likewise, a relatively similar experimentation of polypropylene fiber on concrete was carried out by Islam & Gupta (2016) with fiber content varied from 0.1% to 0.3% by volume of specimen in contrast to a reference mixture. Similarly, Bagherzadeh et al. (2012) conducted an experiment on polypropylene-reinforced lightweight cement composites (LWC) with varying fiber lengths (6mm and 12mm) and fiber proportions (0.15% and 0.35%) by cement weight 4 of mixture compared to unreinforced LWC. In all the mentioned experiments, each concrete cement specimen was prepared and formulated in 28-days period for each test in order to obtain a more accurate set of data. The relative humidity measurements were taken using hygrometer in four different depths of specimen exposed in drying conditions. The tests have shown a decrease in relative humidity for all mixtures with a limit of value set to 75% which varies according to the drying depth of the composition of the mixture. The relative humidity of polypropylene fiber reinforced mortar however, remains significantly high. Similarly, the addition of both polypropylene fibers and PVC plastic grains contribute to maintaining the internal relative humidity for high levels in a longer time period. On the other hand, there have been a decrease in degree of saturation for all mixtures of the formulated mortars which was attributed to the development of the porous network within the material that facilitates the departure of water. The Young’s modulus meanwhile, was shown to be highest at the mortar containing polypropylene fiber particularly on the 1.5% dosage of just the fiber compared to other formulated mortars. Concerning the stated parameters, differential shrinkage was obtained with the use of regular comparator to measure the change in size of samples due to shrinkage contraction. The test revealed that the addition of polypropylene fibers had a remarkable contribution to delaying the phenomenon of shrinkage noting that the formulation containing 1.5% polypropylene fibers had the most effective contribution to reducing the amplitude of shrinkage compared to other formulations. Accordingly, the combined PVC and polypropylene fiber led to a significant reduction of both crack 5 opening and shrinkage magnitudes. In support of these findings, Islam & Gupta (2016) recorded a decrease of 50-99% in plastic shrinkage cracks upon polypropylene fiber reinforcement showing no plastic shrinkage cracks for samples having 0.30% added fiber (by volume) and restrained cracks for 0.10-0.25% added fiber compared to the control sample. Additionally, Bagherzadeh et al. (2012) had similar experimentation outcome revealing that in fact the utilization of polypropylene fibers decreases the shrinkage value of concrete specimens and mentioned that the increase in fiber proportioning seemed to result in a reduction in shrinkage value which consequently reduce cracks. Figure 1 The evolution of the differential shrinkage gradients for different formulated mortars Figure 2 The evolution of crack openings for different formulated mortars 6 Relevant to these findings, it was revealed that the addition of polypropylene fiber decreases the compressive strength of the material by 2% upon 0.1% fiber reinforcement along with an increase in tensile strength by 39% according to Islam & Gupta (2016). Furthermore, based on the experiment conducted by Bagherzadeh et al. (2012), it was indicated that higher proportion and length of the polypropylene fiber amounts to better result in terms of tensile strength and reduction of shrinkage cracks. III. CONCLUSION This paper reported experimental results regarding the phenomenon of cracking that develops in cementitious materials as effect of drying. This study evaluates and provides understanding on the main parameters generating the cracking phenomenon such as internal relative humidity, Young’s modulus, and hydration degree and porosity. Moreover, the aim of this study is to better understand and assess the overall impact of varying formulation and composition on total free shrinkage and crack development. The given findings have led us to conclude the following: Polypropylene fiber and PVC plastic grains reinforcement on concrete significantly reduces both the amplitude of cracking and the shrinkage magnitude with a spike at 40% substitution rate for plastic grains and at 2% for polypropylene fibers. Relative to the drying depth, the development of crack opening and shrinkage decreases proving that water departure induces significant cracking from drying shrinkage. 7 Internal relative humidity must be a fundamental consideration to fully understand the drying phenomenon among cementitious materials along with Young’s modulus and the porosity of the material. 8 References Aqil, M. et al. (2020). Experimental study of the effect of adding polypropylene fibers and pvc waste on cement mortars’ drying shrinkage and crack opening. Retrieved January 30, 2021, from_https://www.academia.edu/43293379/EXPERIMENTAL_STUDY_OF_THE_EFF ECT_OF_ADDING_POLYPROPYLENE_FIBERS_AND_PVC_WASTE_ON_CEMEN T_MORTARS_DRYING_SHRINKAGE_AND_CRACK_OPENING Bagherzadeh, R et al. (2012). An investigation on adding polypropylene fibers to reinforce lightweight cement composites (LWC). Retrieved January 30, 2021, from http://64.71.128.227/papers/Volume7/7.4.3-R.Bagherzadeh.pdf Islam, G., & Gupta, S. (2016). Evaluating plastic shrinkage and permeability of polypropylene fiber reinforced concrete. Retrieved January 30, 2021, from https://www.sciencedirect.com/science/article/pii/S2212609015300789#b0110 Anandan, S. & Sivakumar, M. (2007). Mechanical properties of high strength concrete reinforced with metallic and non-metallic fibers. Retrieved January 30, 2021, from https://www.researchgate.net/publication/223564548_Mechanical_properties_of_high_str ength_concrete_reinforced_with_metallic_and_non-metallic_fibres 9 APPENDIX 1: Results of the Tests Figure 1 The Evolution of the Differential Shrinkage Gradients for Different Formulated Mortars, p.10 (Aqil, et al. 2020) Figure 2 The Evolution of Crack Openings for Different Formulated Mortars, p.10 (Aqil, et al. 2020)
