Introduction to high tensile concrete
Keywords
High Tensile Concrete, HPMC, PAM, MC, Amorphous Calcium Aluminate, High Tensile Shotcrete
High Tensile Concrete (HTC) is a new type of cement-based composite material designed based on the closest packing theory and made by incorporating a certain volume of fiber. It has ultra-high impermeability, mechanical properties, corrosion resistance and fatigue resistance. advantage.
At present, cellulose ether, methylcellulose and polyacrylamide (PAM) are mainly used as admixture materials to achieve high tensile properties of concrete.
Polyacrylic glue is a polymer obtained by homopolymerization or copolymerization of acrylic glue monomer under the action of an initiator. It has the effects of flocculation, drag reduction, dispersion, etc. When PAM is dissolved in water, it dissociates into multi-charged large molecular weight ions in the water. The strong repulsion between the same charges causes the coil-like macromolecules to turn into curves, increasing the viscosity of the solution. When there is a strong external force, the macromolecules will deform back into a coil shape, causing the viscosity to decrease.
Hydroxypropyl methylcellulose ether (HPMC) is a common polymer thickener. The hydroxyl and ether bonds in the molecular chain can combine with free water through hydrogen bonds. When used in concrete, it can effectively improve its cohesiveness. and water retention. HPMC molecular chains are disordered and exhibit higher viscosity at low shear rates; however, at high shear rates, the molecules move in an orderly parallel manner along the direction of the shear force, making it easier for the molecules to slide and the viscosity to decrease. The type and dosage of thixotropic agent have a great influence on cement paste.
The key factor in the workability of high-tensile shotcrete as a reinforcing material lies in adjusting the rheological properties of freshly mixed HTC so that it has a large yield stress and moderate plastic viscosity. In addition to adding the above-mentioned thixotropic agent, in order to improve the early strength performance and ultra-rapid setting performance of shotcrete, amorphous calcium aluminate is also one of the necessary admixtures.