Surface Modification Of Recycled Fine Aggregate And Application Research Used In The Mortar

According to statistics, only the construction waste generated by the earthquake in wenchuan was nearly 600 million tons. The construction waste existed not only take up a lot of land resources,but also could cause serious pollution of the local water, air, soil,and so on.Along with the accelerating pace of China’s national economy, the rational use of building Garbage had become an urgent problem. The construction waste after crushing, cleaning,grading and other processes can obtain recycled aggregate for the preparation instead of natural aggregate concrete. However, compared to the natural aggregate concrete,the mechanical properties, durability of recycled aggregate concrete were poor. Because large amounts of aggregate micro-cracks, pores were existed on the surface of recycled aggregate after crushing produce.In this paper,we focus on the modification of RFA, such as fly ash, slag and other inorganic active admixture, water glass and polyvinyl alcohol, VAE emulsion used. And the properties before and after modification was studied, including the apparent density, water absorption, porosity and crushing index. Of course, the properties of recycled mortar was researched,such as mechanical properties, durability and micro-structure analysis. We can get some results from experimental studies:1. Compared with natural aggregate, RFA had a low density, but water absorption,porosity and crushing characteristics were high. Otherwise, the water absorption of RFA in10 min was 82.7%2. 2. Compared with unmodified RFA sample, after modified by 15wt%slag slurry and5wt% solution of sodium silicate,the water absorption and crushed index of RFA were63.7%,55.3% lower. When RFA modified by sodium silicate solution, we can see that the sodium silicate gel can be cured in its a layer of adhesive film formed on the surface, the surface structure of dense sodium silicate slag powder for hydration plays a certain role, and the absorption of RFA.was reduced.3. When the organic modifier RFA by 10wt% polyvinyl alcohol solution of RFA modified better, the water absorption was reduced, but VAE emulsion has little effect on the water absorption. Modified RFA sample B7,its absorption was decreased by 58.3%.4. Organic-inorganic composite modified RFA sample C6, its water absorption was2.3%, and crushing index value was 8.7%. modification effect of slag powder is more obvious, that may be related to a smaller fineness while higher activity index correlated.5.RFA was pre-soaked 10 minin secondary mixing processes. Compared with the traditional preparation process, its mechanical properties of the mortar in preparation process for the preparation are improved.6. For the thickness of ITZ, the inorganic modification played a certain effect on it.Thickness of samples MA9 is 40μm and reduced by 50% compared to sample H0. The thickness of ITZ of MC5 ~ MC8 were about 20μm ~ 30μm7. For porosity, sample MA9 was 14.9% compared with H1, and reduced about 57.2%.The porosity of samples MB7 was 23.2%. Combined with MB1, the PVA modification improved porosity;8. For the mechanical properties of recycled mortar, the 28 d flexural strength and compressive strength of samples MA9 was increased of 23.7% and 34.7% compared with H1.It can be explained after the modification of slag and water glass,the mechanical properties of RFA was greatly improved.9.For the dry shrinkage performance, after the modification of fly ash, the 28 d dry shrinkage was high..10. For the freeze-thaw performance, the loss rate of recycled mortar after inorganic modification was reduced significantly. The compressive strength loss of sample MA10 was13.6%. The compressive strength loss of samples MB4 after VAE modification was 19.2%and increased by 59.9%.11. For micro-structure, firstly the unmodified RFA,there was a big size of hexagonal plate-CH crystal cement in ITZ, and the presence of large pores between the crystals, and modified RFA- cement in ITZ was only small tabular crystals CH, CSH gel hydration products, such as mutual interspersed compact structure, no significant porosity, pore. Based on the traditional "cement" theory, the RFA micro-structure models was researched.