Smart Additives for Self-Curing Concrete
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Smart Additives for Self-Curing Concrete Konstantin Kovler National Building Research Institute – Faculty of Civil and Environmental Engineering, Technion – Israel Institute of Technology, Haifa, 32000, Israel
ABSTRACT Self-curing, or internal curing (IC), technology has been developed to counteract selfdesiccation and autogenous shrinkage of high-strength/high-performance concrete (HSC/HPC), which is considered the "Achilles' hill" of HSC/HPC [1]. According to ACI [2], IC refers to the process by which the hydration of cement continues because of the availability of internal water that is not part of the mixing water; while the internal water is made available by the pore system in structural lightweight aggregate (LWA) that absorbs and releases water. Recently ACI defined internal curing as “supplying water throughout a freshly placed cementitious mixture using reservoirs, via pre-wetted lightweight aggregates, that readily release water as needed for hydration or to replace moisture lost through evaporation or self-desiccation” [3]. Both definitions address the use of pre-wetted LWA as a self-curing (or internal curing) agent. According to the definition of the RILEM Technical Committee TC-196 [4], IC implies introduction to the concrete mixture a component, which serves as a curing agent. This agent can be either a normal aggregate introduced into the concrete mixture in water-saturated state or a new component (for example, an additive or special aggregate). Similarly to the division accepted in external curing, RILEM TC-196 distinguishes between two categories of internal curing: (a) internal water curing (sometimes called “water entrainment”), when the curing agent performs as a water reservoir, which gradually releases water, and (b) internal sealing, when the curing agent is intended to delay/prevent loss of water from the hardening concrete. Although water-saturated porous aggregate is still the most popular material among IC agents, superabsorbent polymers (SAP), ceramic waste, recycled aggregate and wood-derived products show promising properties. In view of this, self-curing covers not only use of pre-wetted LWA, but also other methods of curing: water curing by means of variety of curing agents introduced in the concrete mix, and also the methods based on internal sealing. The recent achievements in methods and materials for self-curing are reviewed, and the future trends in development of self-curing concrete are discussed. INTRODUCTION Advances in concrete technology over the past years have led to the practical use of highstrength (HSC) / high-performance (HPC) concrete made at low water/cement ratio (w/c). HSC/HPC has not only superior mechanical properties, but also known for its enhanced durability. Greater durability of HSC/HPC makes its use attractive in aggressive environments, significantly reduces maintenance costs and enhances service life [1]. On the other hand, low w/c concrete is prone to early age cracking unless special precautions are taken. The primary reason for the propensity of H
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