Effect of mineral admixture on chemical shrinkage and spectral properties of cement-based materials

Abstract: Chemical shrinkage of cement paste could result in the crack of concrete, which affects the volume stability and durability of concrete. In order to reduce the shrinkage performance of concrete, this paper discusses the effect of common mineral admixture (lithium slag, fly ash, steel slag) on the chemical shrinkage and the spectral characteristics of cement paste, and analyzes the correlation between the chemical shrinkage of cement paste and the functional groups in cement paste. The results are as follows: The chemical shrinkage of pure cement paste and cement paste containing mineral admixtures (lithium slag, fly ash, steel slag) can be roughly divided into 3 stages, namely the acceleration phase (within 100 h), slow phase ( in 100-700 h), and flat stage (after 700 h). When the ratio of water-binder is 0.40 and the admixture dosage is 20% for 3 kinds of admixture, the chemical shrinkages of cement-lithium slag, cement-fly ash and cement-steel slag paste are 81.2%, 97.2% and 91.0%, respectively, and they are reduced by 1.9%, 1.8% and5.0% when admixture content increases from 20% to 60%, respectively. The chemical shrinkages of cement, cement-lithium slag, cement-fly ash and cement-steel slag paste are 24.4%, 32.3%, 26.8% and 29.7% respectively when the ratio of water-binder reduces from 0.40 to 0.30 and the admixture content is 20%. The chemical shrinkage of 4 kinds of paste can be fitted with hyperbolic model, and the correlation coefficients are above 0.98. So, hyperbolic model can be used to predict the final chemical shrinkage of cement paste, but the hydration coefficient value can be chosen according to the ratio of water-binder, and kind and dosage of admixture. The chemical shrinkage and hydration heat are lowered when cement is replaced by the same quality lithium slag, fly ash or steel slag, and the chemical shrinkage of cement-fly ash paste is the biggest, followed by the chemical shrinkage of cement-steel slag paste, and the chemical shrinkage of cement-lithium slag paste is the minimal, which is lower than that of pure cement paste. In addition, water-binder ratio also affects the chemical shrinkage of cement paste and the effect of water-binder ratio is higher than lithium slag, fly ash and steel slag. The spectral characteristic of cement paste is affected by mineral admixture type, dosage of mineral admixture and water-binder ratio, but their influence is not the same, mainly due to the different chemical composition in lithium slag, fly ash and steel slag. The main characteristic peaks of pure cement paste and cement paste containing mineral admixtures (lithium slag, fly ash, steel slag) are 3 647, 2 937, 3 451, 1 651, 2 361, 1 124, 1 418, 451 and 978 cm-1. Through the analysis of the general linear single variable model in SPSS 20.0 statistical software, it is found that the chemical shrinkage of cement paste can be affected by functional groups in the cement paste, and the effect is bigger when the wave number is 1 124, 1 418, 3 451, 3 647 and 978 cm-1. Through the study, it is found that after the same quality mineral admixture (lithium slag, fly ash, steel slag) is used to replace cement, the chemical shrinkage of cement paste can be effectively reduced, and the spectral properties of cement paste can be changed. Therefore, the mineral admixture can be chosen according to the situation of the mineral admixture in actual engineering, so as to enhance the volume stability and durability of cement concrete with mineral admixture (lithium slag, fly ash, steel slag).