Performances of high performance polymer modified concrete for mining engineering
Although ordinary concrete is used in mining engineering, it has many defects such as high brittleness and low flexibility. It is urgent to exploit a kind of high performance polymer modified concrete for mining engineering which has low cost price, high performance, high bond strength, great convenience and excellent durability. Mechanical properties and durability were studied on ordinary concrete, concrete with polyacrylic acid latex and concrete with polyacrylic acid, styrene-acrylic two latexies and silica fume. The results are as follow. First, compression strength of concrete with polyacrylic acid latex is lower than that of ordinary cncrete. And its rupture strength, tensile splitting strength, bond strength and impermeability is higher by 28.6%, 37.5%, 55.3% and 77.2% than ordinary concrete respectively. Second, concrete with polyacrylic acid, styrene-acrylic two latexies and silica fume has higher compression strength than common concrete. At the same time, its rupture strength, tensile splitting strength, bond strength and impermeability is higher by 48.8% 53.1% 73.0% and 83.3% than ordinary cncrete respectively. So, it is called high performance polymer modified concrete. Third, it was analysed by scanning electron microscope. Last, the experiments in a mine shows that its performances and bond strength with tunnels are higher than ordinary concrete while its price is only higher by 0.6% for 1 stere concrete.
Microstructural aspects in a polymer-modified cement
Scanning electron microscopic observations of polymer-free and polymer-modified cements have shown that the polymer particles are partitioned between the inside of hydrates and the surface of anhydrous cement grains. Differential thermal analysis, thermogravimetric analysis, and porosimetry experiments show the retardant effect of the polymer and provide information on changes in porosity.
Hypothesis for Reinforcement of Portland Cement by Polymer Latexes
Vinylidene chloride and styrene-butadiene copolymer latexes are used commercially to reinforce portland cements. Although the technology is well developed, the mechanism of reinforcement is not well understood. A hypothesis is proposed to explain this reinforcement, i.e. (1) latex substitutes for all or part of the water to give the same fluidity at a lower water/cement ratio; (2) latex particles coalesce around each unhydrated (or slightly hydrated) cement grain and aggregate particle to form an interpenetrating network of polymer throughout the structure; (3) microcracks form throughout the structure to relieve the strain introduced by the shrinkage of the portland cement that occurs when the relative humidity falls below 100%; and (4) a propagating microcrack intersects the interpenetrating polymer network to form microfibers spanning the microcrack, sometimes so effectively that propagation is halted, but always so that the microcrack is held together. This hypothesis was supported by scanning electron microscopy of latex-modified cement specimens, as well as by other experiments. More work is needed to determine how each part of the hypothesis contributes to the physical properties of latex-modified cement.