Internal Curing Effect of Pre-Soaked Zeolite Sand on the Performance of Alkali-Activated Slag.

Guang-Zhu Zhang,Xiao-Yong Wang,Yi Han,Han-Seung Lee

doi:10.3390/ma14040718

Guang-Zhu Zhang, Xiao-Yong Wang + Show 2 more

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https://doi.org/10.3390/ma14040718

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Abstract

This study clarifies the effects of pre-soaked zeolite sand as an internal curing material on the hydration, strength, autogenous shrinkage, and durability of alkali-activated slag (AAS) mortars. The liquid-to-binder ratio (L/b) of all of the AAS mortars was 0.55. Sodium hydroxide solution was used as an alkali activator and an internal curing liquid. Calcined zeolite and natural zeolite sand replaced the standard sand at 15% and 30%, respectively. The setting time, autogenous shrinkage, compressive strength, ultrasonic pulse velocity, and surface electrical resistivity were tested. The following conclusions were drawn: (1) The addition of zeolite significantly reduces the autogenous shrinkage of AAS mortar. Compared with the control group, 30% calcined zeolite reduced the autogenous shrinkage by 96.4%. Moreover, the autogenous shrinkage of the AAS mortars was noticed in two stages (a variable temperature stage and an ambient temperature stage), and the two stages split at one day of age. (2) The compressive strength of all of the specimens increased as the zeolite sand content increased, and the highest compressive strength was obtained for AAS combined with 30% natural zeolite sand. (3) Internal curing accelerated the formation of the second peak of heat flow and reduced the accumulated heat release. (4) Calcined zeolite sand delayed the setting time of the AAS mortars. (5) The addition of zeolite significantly reduced the surface electrical resistivity of the AAS mortars. In summary, zeolite sand is extremely useful as an internal curing agent to reduce autogenous shrinkage and to increase the compressive strength of AAS mortars.

Highlights

Zeolite sand is extremely useful as an internal curing agent to reduce autogenous shrinkage and to increase the compressive strength of activated slag (AAS) mortars
Ordinary Portland cement (OPC) is a widely used inorganic binder in modern construction, researchers have considered the possibility of using alkali-activated slag (AAS) to replace some of the ordinary Portland cement (OPC) in construction due to the negative impact of OPC on the environment [1]
Based on the above review of the literature on internal curing, we found the weak points of previous studies to be as follows: (1) SAPs effectively reduce autogenous shrinkage but cause a significant loss of compressive strength; (2) the currently available lightweight aggregates are capable of reducing autogenous shrinkage without causing a loss of compressive strength, but their efficiency in reducing autogenous shrinkage is not satisfactory; (3) pre-soaked lightweight aggregates are mostly studied in OPC systems, while research on their use in AAS systems is very limited

Summary

Introduction

Ordinary Portland cement (OPC) is a widely used inorganic binder in modern construction, researchers have considered the possibility of using alkali-activated slag (AAS) to replace some of the OPC in construction due to the negative impact of OPC on the environment [1]. Because less energy is needed in the AAS production process, carbon emissions can be reduced [2,3]. One of the main reasons restricting the use of AAS is that its autogenous shrinkage is significantly higher than that of OPC [5]. The cement composition and fineness of slag [6,7], the form and quantity of the alkali activator, and the curing conditions [8] are all factors that have been documented to impact cement shrinkage in the production of slag. Researchers have attempted to mitigate the autogenous shrinkage of the AAS system by employing different approaches to decrease the autogenous shrinkage of the OPC, considering the similarity of the autogenous shrinkage between the AAS and OPC systems

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