Mechanical Properties Improvement Mechanism of Silica Fume-Modified Ultrafine Cement Used to Repair Pavement Microcracks

Abstract

With heavy modern traffic and natural factors, cement concrete pavement cracks have become increasingly serious. However, most existing inorganic repair materials for cement concrete pavement cracks have low interfacial bonding strength. Ultrafine cement, silica fume (SF), and other admixtures, which are superfine and used to repair fine early cracks, are prepared as the mending material in our research. Compression strength, bending strength, and interfacial bonding strength are studied, and modification mechanisms are discovered by using a powder X-ray diffraction test, thermal analysis, and micromorphology observation. The result shows that mechanical strength of the stable period is improved with the right amount of mixing of SF, which leads to secondary pozzolanic reaction and makes the microstructure of the paste denser. Meanwhile, a large amount of Ca(OH)2 and water in the interface area are consumed by the secondary pozzolanic reaction, which brings out good interfacial effects with no water film between the new paste and existing concrete. Our experiments show that the pastes with 3–5% SF have better bending strength (15%∼17% improvement) and compressive strength (7%∼9% improvement). Interfacial bonding strength is also increased with a certain amount of SF. Tensile shear bonding strength has been improved more than 4 times when SF dosage is more than 3%. Thus, we recommend a paste with 5% SF as the best mixture to be used to repair cracks.