Study On Preparation And Early Strength Performance Of Hydrotalcite/Fly Ash Composite Grouting Material

There were many kinds of cement additives,early strength additives were more widely used.Early strength agent was widely used because it could greatly improve the early physical properties of cement.The increase of early strength could shorten the production cycle of cement,cement-related products and improve production efficiency at the same time.At present,most of the early strength agents in the market had many defects,such as high dosage and high alkali content,which had a negative impact on the durability and safety of cement and its products.These problems led to the use conditions and scope of early strength agent to be greatly reduced.Traditional early strength agents could be roughly divided into organic,inorganic and composite additives.The inorganic substance had the widest application range,low price and remarkable early strength effect.The most commonly used inorganic salts were chloride and sulfate.They contained a large amount of Cl^-and SO₄^2-,made the fluidity worse and corroded the steel bar in concrete,thus could not meet the pumping requirements and shorten the service life of concrete.In order to solve the cost problem of early strength cement,fly ash could partly replace cement.However,fly ash was the waste gas of coal-fired power plants.If merely add it into the cement,early strength would be reduced to a certain extent.This paper take pure Portland cement as the research object,aiming at the problem of early strength reduction caused by high alkali and high dosage and use of fly ash reducing early intensity.Using pure Ca-Al-Cl LDH as the main early strength material,it was combined with organic-organic early strength agent and inorganic-organic early strength agent respectively.The optimum formula of composite early strength agent was determined by progressive compounding method and orthogonal experiment method respectively,and its effect on physical properties of cement system was studied.The inorganic-organic composite early strength agent and fly ash were used together,determine the formula and study the effect of composite early strength agent on the physical properties of cement-fly ash system.The contribution of each early strength component to the strength performance of different ages is determined by range analysis.The mechanism of early strength is discussed by means of microscopic analysis and physical performance test.The main contents and results are listed as follows:The effect of Ca-Al-Cl LDH on the strength of cement for 1 day was investigated under the conditions of water-cement ratio 0.4,curing temperature 20?and curing humidity 97%,respectively.The optimum content of Ca-Al-Cl LDH was determined to be 2%.Ca-Al-Cl LDH,TEA and TIPA were used as organic early strength agents and PC.The influence of composite on cement early compressive strength was studied.The optimum composition was determined by progressive compounding method:Ca-Al-Cl LDH 2%+TEA 0.02%+TIPA 0.02%+PC 0.2%.The compressive strength can reach 13.56 MPa in one day,23.8 MPa in three days and 33.76 MPa in seven days,which are increased by 87.5%,20.0%and 16.0%respectively in the reference group,and the fluidity can reach 212 mm.The initial and final setting time are 370 min and 425 min respectively.Microscopic analysis showed that the lone pair electrons on the N atom of TIPA and TEA could react with the Fe³⁺,Al³⁺ions in the liquid phase of cement to promote the formation of C-S-H and AFt.Ca-Al-Cl LDH as seed material promotes the reaction of cement clinker,and at the same time ionizes Ca²⁺,Al³⁺,which further promotes the formation of AFt;a large number of C-S-H and AFt make the density of cement block increase,the compressive strength is improved,and the pore size is optimized.The other conditions remain unchanged,orthogonal compounding with CaBr₂,TEA,PC and other components is carried out to determine the best formula:Ca-Al-Cl LDH?2%?+CaBr₂?0.3%?+TEA?0.02%?+PC?0.2%?.Compressive strength reached 14.28 MPa in one day,24.7 MPa in three days and 35.13 MPa in seven days,respectively,which increased 97.5%,24.6%and 20.7%on the basis of the baseline group,30.1%,10.8%and 9.4%compared with the control group.The initial and final setting time were 357 min,370 min and the fluidity was 210 mm,respectively.The range analysis of the compressive strength of each experimental scheme shows that Ca-Al-Cl LDH has the greatest influence on the different ages.By means of XRD,SEM,TG and pore size analysis,it can be found that the composite early strength agent can promote the hydration reaction of cement to produce more AFt,AFm and C-S-H colloids.CaBr₂ makes CH crystal precipitate more easily and promotes the dissolution of C₃S.Ca-A1-Cl LDHS acts as seed to promote the formation of more AFm crystals in clinker.The dissolved Ca²⁺and Al³⁺play an early-strength role,produce more aluminium glue and AFt,form a dense network structure,reduce the cumulative pore volume in cement,and improve the early compressive strength.The optimum content of fly ash in pure cement is 20%.Ca-Al-Cl LDH,TEA and PC were added into the cement-fly ash system containing 20%fly ash to carry out progressive mixing experiments.The optimal experimental mixing ratio was Ca-Al-Cl LDH?2%?+TEA?0.02%?+PC?0.2%?+20%fly ash.Under the optimum mixing ratio,the 1day strength can reach 16.71 MPa,3day strength can reach 25.1 MPa,and 7day strength can reach 36.08 MPa.The rate of the baseline group is 256.1%,126.6%and 124.0%,respectively.The fluidity is 210 mm,and the final and initial setting time are 452 min and 414 min,respectively.Through microscopic analysis,it can be found that fly ash provided a large number of nucleation sites and promoted hydration to form C-S-H colloids.The alkalinity of Ca-Al-Cl LDH promoted fly ash to release active SiO₂ and Al₂O₃,which reacted with CH to form C-S-H,and jointly promoted cement clinker C₃S reaction.Ca-Al-Cl LDH layered double-layer structure and fly ash can absorb free water in the environment and increase the density of the system;more C-S-H produced by fly ash in alkaline environment can refine the pore size of the slurry.Figure[42]Table[18]Reference[95]...