Chemical shrinkage and drying shrinkage of calcium carbide residue-waste red brick powder based cementitious materials pastes

In this study, the chemical shrinkage of calcium carbide residue-waste red brick powder cementitious materials pastes (CWCP) was tested using two different methods， and the shrinkage mechanism of drying shrinkage and chemical shrinkage was analyzed. The products at different stages of material shrinkage were studied by means of Fourier transform infrared spec-troscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric (TG). The results indicated that the chemical shrinkage test method was more accurate after the pastes was sealed. The chemical shrinkage of CWCP can be mainly divided into four stages, shrinkage, expansion, re-shrinkage, stability. An increase in calcium carbide residue (CCR) during the initial shrinkage stage will enhance the alkali concentration, promote the dissolution of the raw materials, and improve the shrinkage value. As the alkali in CCR and the active ingredient in WRBP were consumed, the chemical shrinkage decreased and then increased with the increase of CCR doping in the re-shrinkage stage. Dry shrinkage was manifested as monotonic shrinkage. The increase of CCR content will produce more amorphous gel with high Ca/Si, thus slowing down the drying shrinkage of samples. The drying shrinkage of CWCP accounted for the main part of shrinkage, and the chemical shrinkage value was about 10% to 22% of the drying shrinkage value after 28 days.