Properties Of Alite-sulphoaluminate Cement And Its Application In Marine Protection Engineering

When ordinary concrete works in the ocean,its performance will be affected by the harsh environment.In the early stage of concrete structure design,improving its corrosion resistance as much as possible has important economic and strategic significance for the development of marine engineering.Industrially produced alite-sulfoaluminate cement(ACSA)can be used as the main cementing material for marine protection engineering concrete under this background.ACSA has the characteristics of strong resistance to seawater erosion.Reasonable adjustment of the amount of gypsum significantly improves the early compressive strength of cement and enables its long-term compressive strength to increase continuously.The dense concrete structure greatly reduces the possibility of seawater infiltration and damage,but the fast setting time is not conducive to construction.In view of this,we have studied the influence of different retarders on its performance,and developed a pumping agent suitable for the cement concrete.The prepared ACSA concrete has been successfully used in marine protection projects in Shenzhen,Guangdong and Sanmen,Zhejiang.Research indicates:The increase in the amount of gypsum can continuously improve the compressive strength of ACSA.When the amount of gypsum is 20%,there are a large amount of ettringite mainly in column shape in the early structure of ACSA hydration.The compressive strengths of 4h,28d and 360d were 10.29MPa,58.30MPa and 66.87MPa respectively,and the strength continued to increase in the later period.Both sodium gluconate(SG)and boric acid(BA)can be used as ACSA retarders,but considering the safety of engineering construction,BA is more suitable.When the amount of SG is 0.84%of the cement mass,the initial setting time of the cement can reach 90min,but the compressive strength is greatly reduced.When the amount of BA is 0.67%of the cement mass,the initial setting time of the cement can also reach 90min,and the reduction of compressive strength is small.Through X-ray diffraction,scanning electron microscopy and hydration heat analysis,it can be found that the main way for SG to prolong the setting time of ACSA is to inhibit the growth of ettringite.And when the amount of SG is high,this kind of hindrance will always exist,resulting in a reduction in the aggregation tendency between cement particles,which is the main reason for the reduction of the compressive strength of ACSA.The main way for BA to prolong the coagulation time of ACSA is to inhibit the dissolution of Ye'elimite phase.As the hydration progresses,the calcium-based boric acid layer formed by the BA on the surface of the cement particles dissolves.This weakens the ability to suppress the dissolution of the Ye'elimite phase,resulting in rapid progress of the hydration reaction.The adaptability of the polycarboxylic acid-based water-reducing agent to ACSA is relatively good,and sorbitol as the slump retention component of the ACSA pumping agent is relatively good.When the ratio of ACSA special pumping agent is polycarboxylic acid water-reducing mother liquor 30%+sorbitol 20%+saturated BA solution 50%,the initial and 1h fluidity of cement paste is 287mm and 280mm,and loses fluidity at 6h.The reasonable mix ratio of C40ACSA concrete is cement 400kg/m~3,sand 835kg/m~3,crushed stone975kg/m~3,stone powder 30kg/m~3,water 160kg/m~3,pumping agent 5.2kg/m~3,BA3.2kg/m~3.At this time,the initial state of the concrete is the best,and it can ensure the minimum slump loss of 3h.The 1d and 28d compressive strengths of the concrete are 47.7MPa and64.3MPa,respectively.The concrete prepared by ACSA completely meets the requirements of high early strength and continuous strength increase in marine protection engineering.The engineering demonstration results of Shenzhen Bay show that the prepared ACSA concrete 1d,28d and 90d compressive strength can reach 38.7 MPa,65.8MPa and 78.6MPa,respectively,which meets the engineering requirements.The engineering demonstration results of the Sanmen Nuclear Power Station show that the 3d and 28d compressive strength of the prepared ACSA concrete can reach 48.5MPa and 56.2MPa,respectively,meeting the requirements of the project.