Ang Su,Yujiang Wang,Rui Wang,Yang Chu,Wen Xu,Qian Tian,Sen Yao,Qingyu Meng,Wenbin Wang
Internal curing is an effective method to reduce the autogenous shrinkage of cementitious materials. Besides, the increasing in relative humidity (RH) due to the internal curing also reduces the coefficient of thermal expansion (CTE), which is beneficial for enhancing the anti-cracking performance of cementitious materials. In this paper, effects of superabsorbent polymers (SAP) on the microstructure and performance of cementitious materials were investigated. The superabsorbent polymer (SAP) changes the time and spatial distribution of water in cementitious materials, so it should have an influence on the microstructure of cement matrix, thus affecting the performance of cementitious materials. Results indicate that the CTE of concrete increases over time, while that of concrete with SAP shows a completely different behavior. In 0.1 % SAP system, the CTE increases slowly over time after about 2days, while in 0.2 % SAP and 0.3 % SAP systems, the CTE is nearly stabilized during the test period. Low-field nuclear magnetic resonance (LF NMR) results indicate that the SAP decreases the number of empty capillary pores and increases the total porosity, which inhibits the increase of CTE over time. The dosage of SAP plays an important role in enhancing the internal curing performance. By increasing the dosage of SAP, the number of empty capillary pores decreases, the saturation degree of capillary pores rises, and consequently, the CTE and autogenous shrinkage of concrete are reduced.
Internal curing agents (ICA) based on super absorbent polymer have poor alkali tolerance and reduce the early strength of concrete. An alkali tolerate internal curing agent (CAA-ICA) was designed and prepared by using sodium carboxymethyl starch (CMS) with high hydrophilicity, acrylic acid (AA) containing anionic carboxylic group and acrylamide (AM) containing non-ionic amide group as the main raw materials. The results show that the ratio of CAA-ICA alkali absorption solution is higher than that existing ICA, which solves the low water absorption ratio of the ICA in alkali environment. The water absorption ratio of CAA-ICA in saturated Ca(OH) 2 solution is 95.8 g·g −1 , and the alkali tolerance coefficient is 3.4. The application of CAA-ICA in cement-based materials can increase the internal relative humidity and miniaturize the pore structure. The compressive strength of mortar increases up to 12.95% at 28 d, which provids a solution to overcome the reduction of the early strength.
Abstract The eco-friendly and low-cost poly(itaconic acid)/poly(sodium allyl sulfonate) (PIA/PSAS) new superabsorbent polymers (SAP) were prepared based on the monomers of itaconic acid (IA), sodium allyl sulfonate (SAS) and the cross-linking agent of N , N′ -methylene bisacrylamide (MBA) by aqueous solution process. Moreover, the expanded vermiculite (EV) particles were used as reinforcement for SAP. The absorption behaviour of SAP in different liquids were studied by the teabag method, including deionized water, 0.9% NaCl solution and cement filtration. The results showed that SAP could reach the optimal liquid adsorption state under certain experimental conditions such as the molar ratio of IA/SAS as 2:1, the IA neutralization degree of 70%, the cross-linker dosage of 0.6%, and the EV content of 2.0%. The morphology and structure of the synthetic SAP were characterized. Furthermore, the effects of SAP type and content on concrete properties were evaluated. Results showed a reduction in shrinkage and revealed SAP particles acted as miniature reservoirs lead to cure concrete internally by supplying water during hydration. The EV particles reinforced SAP composite slightly and alleviated the negative influence on the compressive strength of concrete relative to PIA/PSAS. This designed SAP showed its potential to be used as an internal curing agent for concrete due to its ability to provide comprehensive protection against shrinkage and fracture. Graphic abstract
危险品化学品经营许可证（带存储）