Internal Curing in High Strength Mortars with Tea Waste Particles: Evaluation of Early Age Shrinkage, Physical and Durability Properties

Abstract

High strength and high performance concretes are made with low water-binder ratios and thus susceptible to shrink at the early ages. Such shrinkages take place due to quick hydration that lead to loss of moisture in the fresh composites. Such deficiency of moisture causes change in volume of concrete and ultimately leads to cracking. To overcome this problem, internal curing technique commonly done in high strength and high performance concretes with pre-saturated porous lightweight aggregates, super absorbent polymers and other absorbent materials to keep such concretes moist for longer times to delay hydration process and to minimize the effect of early self-desiccation. In this study, pre-saturated porous earl-grey black tea waste (TW) particles were used as major internal curing agents. In addition to that, perlite and super-absorbent polymer (SAP) particles were also used for comparison purpose along with tea waste particles. The early age properties, physical and microstructural properties, and the durability related properties of high strength mortars were evaluated during this study. The early age properties included mortar flow, setting times, chemical and autogenous shrinkages, heat of hydration/internal temperatures, and internal relative humidity of the specimens. The physical properties comprised quality parameters, such as weight, absorption and porosities, bulk and apparent densities, mechanical parameters, like, compressive, split tensile and flexural strength, and non-destructive parameters, for instance ultrasonic pulse velocity and dynamic young’s modulus of elasticities. Moreover, the evaluated microstructural properties included X-Ray diffractometric, Thermo-gravimetric analysis and derivative thermo-gravimetric analyses, Fourier transform infrared and scanning electron microscopy of different mixes. Finally, the durability properties, viz., chloride penetration, carbonation attack, acid attack and freeze-thaw of specimens were also assessed to recognize the influence of tea waste and other curing agents on durability performance. To investigate all these parameters, tea waste and perlite particles with two distinct size particles and contents were added in different mixes, whereas, the SAP particles were used in two separate amounts as received form. Ordinary Portland Cement (OPC) and silica fume (SF) were added in mixes as primary and secondary binders, respectively. Natural river sand was used as fine aggregate in all mixes. The results revealed that the addition of tea waste particles in mortars reduced the mortar flow, early age shrinkages (chemical and autogenous shrinkage), heat of hydration and strengths as compared to the control mix, mostly at very early ages. Similar performance was observed for other curing agents as that of tea waste particles but their effectiveness against mitigating early age shrinkage was lesser, especially for perlite particles. Whereas, the setting times, internal relative humidity, absorption and porosities increased with the addition of curing agents. Furthermore, tea waste particles presented slightly poor performance against chloride penetration and acid attack as compared to other curing agents; however, in case of carbonation penetration and freeze-thaw performance, the adverse impact of tea waste particles was negligible. Since the incorporation of silica fume improved the mechanical, physical and microstructural, and durability properties significantly, however, its inclusion had negative impact on controlling early-age shrinkages (chemical and autogenous shrinkages), heat of hydration and internal relative humidity (RH). It is revealed that the addition of pre-saturated earl-grey tea waste particles help to prevent/minimize the early-age shrinkages i.e. chemical and autogenous shrinkages and reduce the heat of hydration by delaying hydration process at very early ages, however, the strength became lesser up to age of 28 days, and found to be increasing at the age of 90 days. Furthermore, the specimens made with coarser particles of tea waste and perlites were found useful to control early age shrinkage and hydration than the finer ones and vice versa for the strengths. It is concluded that the coarser particles of tea waste and perlite particles could be used in high-strength mortars to mitigate the early age rapid heat of hydration with slight reduction in the mechanical and physical properties at early ages. However, the strength can be recovered at later ages or the addition of little amount of supplementary cementitious material.