| Self-compacting concrete(SCC) has good fluidity, and achieves full density without vibration ramming. It is less prone to stratification and segregation, especially in columns that have high reinforcement density and other structures where vibration ramming is not viable. Despite these advantages, it has a low water to cement ratio and the high powder dosage can produce a significant increase in both autogenous shrinkage and drying shrinkage. If not treated appropriately, the SCC is prone to produce shrinkage cracking during the hydration and hardening process, resulting in a serious decline in the durability of the concrete.This studies show that the addition of proper amounts of maintenance materials,such as super water absorbent resin and light aggregate, can effectively reduce the autogenous shrinkage of the concrete. However, super absorbent resin is expensive and lightweight aggregate can easily cause segregation in SCC.Hence, this study tried using sewage sludge containing flocculent material to reduce shrinkage. The use of undisturbed sludge or dry sludge as a curing agent was compared with the use of super water absorbent resin as a means of reducing shrinkage. The study focussed on adding original sludge, dry sludge, pre wetting water tree fat(SAP) and the shrinkage reducing agent(SRA) compound. Their effects on freshly mixed hardening SCC were assessed by measuring: the increase in water temperature; strength; internal relative humidity change; autogenous shrinkage and total shrinkage.Research results show that:(1) Adding undisturbed sludge to SCC decreased growth slump, but there is help to improve the SCC bonded together and soil and water conservation; Added with drysludge of SCC workability has little effect; the introduction of water phase at the same time, compared with the undisturbed sludge, added pre wet SAP is conducive to enhancing the SCC of liquidity; Added undisturbed sludge, sludge drying and pre wet SAP in extended SCC initial setting time, adding the sludge drying, the impact on the initial setting time is particularly significant.(2) Compared with the contrast concrete, the single-doped undisturbed sludge,dry sludge, SAP and SRA all lead to the early strength of SCC and the decrease of SAP is more obvious; But in the 28d~60d, its strength growth rate is higher than that of concrete, the 60 d intensity is even higher than that of the concrete. The reason may be the internal curing of high strength SCC, which helps to reduce the autogenous shrinkage and prevent shrinkage cracking.(3) Compared with the contrast concrete, the effect of the added undisturbed sludge on the relative humidity of the low water-cement ratio of the cement concrete is very obvious, and the relative humidity in the early stage of hydration caused a significant decrease; With the addition of SRA, similar exception is still present, but the amplitude is significantly decreased, and the reasons are not clear, it needs to be further studied. Single mixed with dry sludge and wet SAP are not found abnormal,the addition of SAP is helpful to reduce the self-drying degree of low water cement ratio.(4) The autogenous shrinkage of SCC can be reduced by mixing the oundisturbed sludge and dry sludge, but the change of the content of SCC is not obvious, and The increase of content will lead to increased autogenous shrinkage,which may be caused by the poor uniformity of the sludge. However, the SCC can be significantly reduced by SAP, and with the increase of the amount of prewet SAP, its autogenous shrinkage will gradually decrease.(5) The composite addition of undisturbed sludge, dry sludge and SRA was carried out, and compared with the single SRA, the original sludge, the dry sludge and the pre wet SAP, the autogenous shrinkage decreased. But the sludge inhomogeneity of flocculation components still lead to its influence on the rule of autogenous shrinkage changes with the content is not obvious, Even since the phenomenon ofshrinkage increase with volume increase. SAP and SRA can further reduce the autogenous shrinkage of SCC.(6) Single doped undisturbed sludge of SCC total shrinkage have little impact;single doped drying sludge, content value can reduce SCC of the total shrinkage, but the incorporation of the sludge solid content is 0.2%, but result the total shrinkage increased significantly, the volume changes of SCC total shrinkage is poor; and single doped pre wet SAP can significantly reduce the SCC of the total shrinkage, the shrinkage rate of up to 26%. The original sludge, drying sludge and pre wet SAP are added to the SRA composite, based on adding the internal curing material,it can further reduce the total shrinkage. |
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