Influence of Superplasticizer Type and Dosage on Early-age Drying Shrinkage of Cement Paste with Consideration of Pore S
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https: //doi. org/10.1007/s11595-020-2318-1
Influence of Superplasticizer Type and Dosage on Early-age Drying Shrinkage of Cement Paste with Consideration of Pore Size Distribution and Water Loss QIAN Xiaoqian, YU Congdi, ZHANG Lifeng, QIAN Kuangliang, FANG Minghui, LAI Junying (College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058, China)
Abstract: We introduced a parameter rs (the radius of the pores where the meniscus forms), which is composed of two factors, i e, water loss and cumulative pore size distribution (PSD), to provide a better explanation of the influence of superplasticizers(SPs) on early-age drying shrinkage. In our experiments, it is found that the addition of three types of SPs leads to a significant increase in the early-age drying shrinkage of cement paste, and drying shrinkage increases with the dosage of SPs. Based on the results above, we further studied the mechanism of the effects of SPs on the early-age drying shrinkage of cement paste by PSD and water loss, which are two components of rs. The experimental results indicate that rs can be a better index for the early-age drying shrinkage of cement-based materials with SPs than a single factor. In addition, the effects of SPs on other factors such as hydration degree and elastic modulus were also investigated and discussed. Key words: superplasticizer; early-age drying shrinkage; water loss; pore size distribution
1 Introduction Chemical admixtures are added to concrete to improve its properties. For instance, the addition of superplasticizers (SPs) to concrete enhances the workability, mechanical properties, and durability of the concrete, while maintaining a low water-tocement (w/c) ratio. During recent decades, progress has been made in the development of different SPs with various dispersing capacities and the application of them to cement-based materials: naphthalene sulfonate formaldehyde polycondensate (NSF) and comb-like polycarboxylate (PCE) SPs are the two categories that are most frequently adopted in modern cement-based materials[1]. The impacts of SPs on the properties of cement pastes and concretes, including cement hydration and strength development, have been extensively studied for many years, and it remains a significant field of research[2-4]. The shrinkage of concrete takes place in two distinct stages: early age and late age. Early-age shrinkage © Wuhan University of Technology and Springer-Verlag GmbH Germany, Part of Springer Nature 2020 (Received: Aug. 10, 2019; Accepted: Nov. 22, 2019) QIAN Xiaoqian(钱晓倩): Prof.; E-mail: [email protected] Funded by the Key Research and Development Program of Zhejiang Province in 2018 (No:2018C03033-1)
is critical since the strain capacity of concrete is at its lowest in the early hours, i e, immediately after casting. Further, in early hours, the sensitivity of concrete to internal stresses is the highest. Research into the early-age shrinkage performance of cementbased materials has gradually received attention[5-8]. In addition, early-age
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