The Damage Characteristics And The Mechanical Properties Of Reinforced Composite Cement Soil In Cold Areas

The goal of the research is to develop"green"construction materials, i.e. to develop a new construction material– composite cement soil using the local materials such as soil, mine residues and industrial wastes. A composite cement material with silt clay was developed to adapt to the cold areas, and the optimal ratio of the composites was obtained. The experiments and tests of strength, endurance, damage, microstructure, etc. were performed. The interactions of composite cement material with soil, water, cement grout were analyzed. The solidification of the composite cement was studied and the damage characteristics were analysised as well, which provide the experiment data and theory for further study and application.The mechanical properties of ordinary cement such as compressive resistance, indirect tensile resistance, and the endurance property such as freezing resistance, impermeability were tested, the main factors to impact the properties of ordinary cement were determined. 8 materials were selected as the cement additives through the alternative comparison. Each additive was tested for the cement soil. The experiment comparison was done for all the additives with the 2 important indexes, i.e. strength and freezing resistance. The impacts and the property improvement of each additive were summarized. The main factors and their importance that affect the strength and freezing resistance of cement were determined by orthogonal test. An optimal mix ratio of the composite material with better quality and eocnomic cost was developed through observation,variance analysis and complementary experiments, the mix ratio is: cement: lime: silica fume: Na2SO4: surfactant = 10:1:3:0.5:0.1. The composite material mixed with soil, water in certain ratio is so called composite cement soil.In order to varify and test the strength and endurance of the composite cement soil, the unconfined compression resistance, indirect tensile resistance, freezing resistance, and frost heave were tested in the lab with different additive quantity, different curing periods, and the comparison analysis with ordinary cement was performed. The results show that the mechanical properties and endurance of the composite cement soil are significantly better than that of ordinary cement.The strength prediction models of composite cement soil and ordinary cement considering all impact factors were developed, and the deformation properties of the two materials were analysised. The constitutive equation of descending and ascending of stress and strain of ordinary cement and the composite cement soil were derived.The microstructure of the composite cement soil was studied with the SEM experiment, the interactions of the composite material with soil, water, cement grout were analyzed, based on the analysis, the solidification of the composite cement soil was analyzed, the inherent nature that the strengh of the composite cement soil was better than that of ordinary cement was reasonablly explained. The damage microstructure and damage evolution of the composite cement soil was analyzed based on the deformation and damage tests in the lab, the elastic and plastic damage model under uniaxial compression stress was developed.