Study On Manufacture And Properties Of Geopolymer-based Coral Concrete

Marine engineering concrete is an important foundation for the development of the marine economy.The use of coral to prepare concrete in the oceanic environment of the South China Sea will effectively solve the problem of aggregate shortage in engineering construction.However,coral aggregates are light-weight,porous,rough in surface and rich in marine salt and sediment.The properties of coral aggregates affect concrete workability,mechanical properties,volume stability and durability.Moreover,the existing cement-based coral concrete has poor corrosion resistance and strength due to the poor stability of cement hydration products in marine environment,the high connectivity porosity and low strength of coral aggregate,and the weak structure of interface transition zone.In this paper,geopolymer-based coral concrete with good mechanical properties was manufactured by optimizing the proportioning parameters of geopolymer and chemically micro-corroded coral aggregate.The main work carried out in this paper and the main conclusions reached:?Numerical description of physical,chemical and morphological properties of coral aggregate.?1?The basic physical and chemical properties of coral aggregates were measured.The coral aggregate is a calcium aggregate with a mineral composition of aragonite;the coral aggregate has a unique tree-shaped and rod-shaped particles compared to the limestone aggregate,and it has a strong water absorption?>12%?.The internal pore structure of coral aggregates can be roughly divided into ant nests,pore clusters and core-shell structures.The maximum porosity calculated by using IPP software ranged from47%to 53%.?2?The morphology of coral aggregates was quantified by sphericity,angular number,index of aggregate particle shape and texture.The average sphericity distribution of coral aggregates ranges from 0.5 to 0.6;the angular number AN of single-grain coral aggregates is 2.4-3.0 times larger than that of the same-grain limestone aggregates;the IAPST of coral aggregates and limestone aggregates is between 31.6-34.3 and 18.6-19.6 under the same-grain size.The texturel index TI,4.75 mm¹6 mm and 16 mm³1.5 mm size coral aggregate are 16.18 and 15.88 respectively,while TI of limestone aggregate is only 1.22and 1.17,which can be better applied to evaluate the surface roughness of coral aggregate.?Chemical micro-corrosion of coral aggregate and its properties?1?Corrosion treatment of coral aggregate is carried out by using acetic acid concentration and acid immersion time as variable conditions.With the increase of acetic acid concentration and soaking time,the quality loss of coral aggregates gradually increases,while the flexural and compressive strengths increased first and then decreased.Under the conditions of 1%⁵%?C?mass fraction acetic acid concentration and 30⁹0min?T?soaking time,the 7d strength of coral concrete showed the maximum value of C3T60micro-corrosion parameters.Under the same soaking time,the flexural and compressive strength of C5T60 decreased by 15.4%and 7.9%compared with that of C3T60,while at the same concentration,the flexural and compressive strength of C3T90 decreased by 6.3%and 6.8%respectively compared with that of C3T60.?2?Exploring the structural characteristics of chemical micro-corroded coral aggregates.An increase in acetic acid concentration and soaking time will increase the connectivity inside the coral aggregate and reduce the strength of the aggregate.The best parameters for coral aggregate acid treatment is C3T60.?Study on mixing ratio parameters and properties of geopolymers?1?Response surface methodology?RSM?was used to optimize the mixing ratio parameters of geopolymer paste.The response surface method is suitable for fitting the second-order response surface model of slag content W_SC,alkali activator modulus M and alkali activator R_AS.The interaction between slag content and activator modulus is very significant.The compressive strength of geopolymer paste increased with the increase of slag content,and increased first and then decreased with the increase of activator modulus.?2?The performance changes of five groups of parameters at the end point and the center point of response surface were explored with different maintenance systems.The specimen under seal curing has higher strength,smaller shrinkage and fewer cracks than that under dry curing.Considering the strength and shrinkage characteristics,the optimum mixing ratio of geopolymer paste is determined:W_SCC is 50%?fly ash/slag?slag,M is 1.4modified water glass,R_ASS is 50%by mass,and the curing condition is sealed curing.?Manufacture of geopolymer-based coral concrete?1?Concrete was manufactured by using coral aggregate treated with optimal chemical micro-corrosion parameter and geopolymers with optimized ratios.The stirring step of the geopolymer-based coral concrete is as follows:1)firstly preparing the geopolymer mortar;2)then adding coral aggregate twice,mixing to present a good state of coarse aggregate coated with mortar after adding aggregate for the first time;3)adding the second time,and stirring until the concrete shows a good flow state and then molding.?2?Geopolymer-based coral concrete with different volume sand ratio was prepared.The compressive strength of concrete increased first and then decreases with the increase of volume ratio of sand from 45%to 54%in 28 days.48%ratio has suitable workability,and its compressive strength in 3 days and 28 days is 24.0 MPa and 49.7 MPa,respectively.?3?The compressive strength of geopolymer-based coral concrete is improved by the methods of coefficient of surplus paste,coated aggregate and fiber reinforcement.The 3-day maximum compressive strength of the three lifting technologies reached 39.0 MPa,35.0MPa and 42.0 MPa,respectively,while the maximum compressive strength reached 54.2MPa,65.1 MPa and 74.2 MPa at 28-day age,respectively.The concrete prepared by the methods of coated aggregate and fiber reinforcement can reach the strength grade standard of C60.At the same time,the ductility of geopolymer-based coral concrete can be improved by adding fibers.