Research On Preparation And Properties Of Calcium Sulphoaluminate Cement Based ECC

The early high strength of repair material is essential for the military protection engineering and the urgent repair project.Engineered Cementitious Composites(ECC),as the repair material,due to its slow strength development and large drying shrinkage,is not conducive to the repair construction.Moreover,considering the influence of natural environment and regional differences,various temperature environments have great effects on the perfomances of repair material,which is not easy to meet the requirements of restoration engineering.In order to prepare the repair material with high early strength and low dry shrinkage at different temperatures,ECC was prepared by sulphoaluminate cement(CSA)and its mechanical properties were studied.Firstly,the workability and mechanical properties of CSA in-10~oC~40~oC were adjusted by the?-naphthalene superplasticizer(NS),calcium nitrate(CN),lithium carbonate(LC),gluconate sodium(SG),and borax(B).The aim of that was to control the setting of CSA and ensure the high early strength of CSA.Secondly,the effects of polyvinyl alcohol(PVA)fiber content and fly ash(FA)content on the compressive strength,bending strength,drying shrinkage,and fracture behavior of CSA-ECC were studied systematically.The results showed that:(1)At 20~oC,when the content of NS was 0.9~1.2%,the final setting time of CSA was20~30min;the compressive strength of mortars was higher than 30MPa and 70MPa at2h and 7d respectively.At 0~oC,when the content of LC-AS was 1.2~1.5%,the final setting time of CSA was 20~30min;the compressive strength of mortars was higher than 20MPa and 50MPa at 2h and 7d respectively.At-10~oC,when the content of LC or LC-AS was 0.9~1.5%or 1.9~2.5%,the compressive strength of mortars was higher than 10MPa and 30MPa at 2h and 7d respectively.At 40~oC,when the content of SG-B was 0.2~0.4%,the final setting time of CSA was 30~50min;the compressive strength of mortars was higher than 30MPa and 70MPa at 2h and 7d respectively.(2)At 20~oC,the use of NS could increase the formation of ettringite(AFt)in early hydration of CSA.However,the improvement effect reduced with time.At 0~oC,the use of LC-AS could enhance the formation of AFt significantly in early hydration of CSA.At 40~oC,the use of SG-B could decrease the formation of AFt.However,the negative effect reduced with time.(3)The early compressive strength of CSA-ECC can reach to 20~40 MPa by changing the content of PVA fiber and FA.The flexural strength of CSA-ECC could be enhanced by the addition of PVA fiber significantly.The mechanical properties of CSA-ECC could be decreased by the increase of FA content.In comparision with the traditional ECC,the drying shrinkage of CSA-ECC was significantly reduced by more than 80%.Meanwhile,the increase of FA content can reduce the drying shrinkage of CSA-ECC.(4)The strain hardening behavior of PVA fibers was observed during the loading process of CSA-ECC.When the content of PVA fiber was 1.5wt.%and the content of FA was 40wt.%,the strain of CSA-ECC at complete failure was larger than that of traditional ECC.There were fiber pull-out,fiber pull-out and bond interface failure in the loading process of CSA-ECC.