Research On Properties Of Mixing-foaming Made Foam Concrete

At present, there have already been plenty of studies concerning about the heat conductivity coefficient and the strength of foam concrete. The technique of improving properties of foam concrete by adding various additives, admixtures and changing the foam amount is getting increasingly mature, as well as he theory about the relationship between the air-void structure and the properties. However, as an inorganic porous material, there comes growing problems of durability, especially the problems of water resisting properties. Since considerable amount of water is consumed by cement hydration and evaporation during the curing process, plentiful capillary pore are left in the cement based matrix, causing larger water absorption than organic materials of the same function. This has become a choke point of improving its durability such as frost-resistance, corrosion resistance etc. As for foam concrete, the additional artificial voids make its water resistance behavior much more complicated. Therefore, it is imperative to figure out the effect of raw material, preparation technics and artificial voids on the water resistance of foam concrete.Mix foaming process was employed to prepare foam concrete specimens in this work. Characters of their cement matrix were varied through changing the water to binder ratio, additive amount, materials mixing order and curing conditions. Tests were carried out for evaluating the dry density, true density, water absorption and resistance to freezing, dry-wet cycle and sulfate corrosion. Air-voids were classified to big, middle and small as three grades according to sectional area of the voids. Image analysis was taken out for measuring characteristics of these voids, such as porosity, size and distribution.The results showed that, in terms of influence of raw materials and preparation technics, specimens with different water resistance behaviors could be prepared:when water to binder ratio was 0.7(or 0.78), water absorption per volume was minimized; when water to binder ratio was 0.54, the water absorption per mass was minimized while the resistance to freezing, dry-wet cycle and sulfate corrosion were optimized. Taking an overall consideration, smaller water to binder ratio will probably benefit for the water resistance. In addition, when the mixing amount of rubber powder was 0.23%, water absorption was minimized and resistance to dry-wet cycles was improved, while when the mixing amount of rubber powder was 0.29%, the freezing resistance was optimized and mixing amount of 0.11% benefited the most for sulfate corrosion resistance. What's more, the minimum water absorption and the best sulfate corrosion resistance were also acquired through mixing order of premix H2O2 and later mix rubber powder while different mix order of rubber powder led to the highest resistance to freezing and sulfate corrosion. On top of this, preservative film and humid circumstance contributed to obtaining the lowest water absorption and strength loss during free-thaw cycles and to reaching the highest sulfate corrosion resistance, while the opposite humid condition benefited to the smallest freeze-thaw strength loss rate and the highest resistance to dry-wet cycles.It was also concluded that, beyond raw material and preparation technics, air-voids' characteristic was another important factor for water tolerance of foam concrete. When average big pore size and roundness were respectively 0.816mm and 1.077, and additionally the porosity ratio of other voids to the big voids was 36.04 and standard deviation of big voids average size was 0.29, the water absorption was minimized, as well as both freeze-thaw loss rates when average pore size of non-big voids was 0.22mm, and when the pore size standard deviation of small void and middle voids were respectively 0.069 and 0.1. When there was no open-void and average roundness of non-big voids was 1.04 and when the standard deviation of average big voids size was 0.23, the dry-wet strength coefficient was optimized, as well as the anti-corrosion coefficient of compressive strength when the average roundness of big voids was 1.092 and when the porosity ratio of middle voids and small voids was 2.82.On basis of single influencing factor investigation on its relationship with water tolerant, orthogonal analysis was employed to estimate the most remarkable one for each key indicator of water resistance ability. As a result, they were interaction of water-binder ratio and rubber power mixing amount, water-binder ratio and H2O2 mixing amount respectively for the water absorption per volume, freeze-thaw strength loss rate, compressive strength anti-corrosion coefficient. Besides this, a method of classifying the voids according to the sectional area was put forward in this work and the numerical relationship between the air-void characters and each indicator of the water resistant ability was built, which provided the theoretical basis for improving the water tolerant of foam concrete.