Research And Application On Polycarboxylate Superplasticizer Of Controlled Function

Polycarboxylate superplasticizer is the third generation water-reduce after naphthalene superplasticizer and lignin.With the high dispersibility and holding dispersibility,the polycarboxylate superplasticizer,which is widely used in construction of highway,railroad,water conservancy and building,is the direction of development of water-reducer.In the paper,financial supported by China "863" Program "2005AA332010" and "973" Program"2001CB610704-3" from the Ministry of Science and Technology and the "2007-k4-3" from Ministry of Construction of the P.R.China,the synthesis and application of polycarboxylate superplasticizer have been researched.Optimum conditions of synthesis middle-monomer and water-reducer has been confirmed;Effect of molecular structure on hydratation of cement clinker mineral phase and Portland cement have been researched to realize the controllability function;The assume of preferential adsorption has been put forward to prepare the low-cost water-reducer and use in the ready-mixed concrete;Mechanism of three generations water-reducer has been compared.The main work and results are listed as follow:1.Researching the synthesis technology of middle-monomer and polycarboxylate superplasticizer to make sure the optimum conditions and also constructing the production line:(1) The inhibitor for methacrylic acid is beforehand prepared by organic-inorganic composite. The inhibitor has good performance of stability that conversion rate of esterification can reach 99%(2) The optimum conditions of synthesis of middle-monomer:when the addition of activator is 5-6%,proportion of acid and alcohol is(1.15-1.2):1,toluene is 50%,and the temperature is 120℃.The optimum conditions of synthesis of water-reducer:when the addition of initiator is 5-7%,the temperature is 80℃,and it reacts for 7-8h,the copolymer has good dispersibility and holding dispersibility.(3) Introducing amphiphilic balance(P₀),hydrophilic balance(k),amphiphilic matching coefficient(λ),the amphiphilic balance and comb-shaped copolymers of the polycarboxylate superplasticizer have been researched.In some condition,the matching coefficient can confer the dispersing ability and monomer matching before we synthesize the copolymer.2.Research the effect of molecular structure on hydration of cement clinker mineral phase and Portland cement and establish the method of controllability function(1) Polycarboxylate superplasticizer accelerates the transformation from 2CaO·Al₂O₃·8H₂O to Al(OH)₃ and 3CaO·Al₂O₃·6H₂O.It restrains hydration of C₃A the as a whole.The ability to delay hydration of C₃A becomes strong with little molecular weight and less grafting density of long-side chain.The big molecular weight of long-side chain is advantaged to transformation of C₂AH₈ to C₃AH₆.The little molecular weight of long-side chain is advantaged to better crystallization of C₃AH₆.(2) Polycarboxylate superplasticizer restrains hydration of C₃S and formation of CH at 1d.With increase addition of molecular weight of long-side chain,ability to restrain hydration becomes weaker.With grafting density increasing of long-side chain,ability to restrain hydration becomes strong.It accelerates formation of CH,and has little ability to restrain hydration of C₃S at 7d.Water-reducer with little molecular weight of long-side chain is advantage to crystallization of CH.No matter how to adjust molecular weight and grafting density of long-side chain,weight of CH in hydration products is little change,but more than control.It mainly effects the formation of CSH at 7d.The ability to restrain hydration nearly disappears at 28d.The bigger molecular weight of long-side chain is,the weaker ability to hydration at 28 d is.The little molecular weight of long-side is advantage to form the CH, but the more grafting density of carboxyl accelerates formation of CSH at 28d.(3) Method of Controllability function of KH:carboxyl and gather oxygen ethylene,which are the main groups of polycarboxylate superplasticizer,has primary effect on the performance. To adjust grafting density and molecular weight of long-side chain can achieve to control dispersibility and holding dispersibility,setting time,air-entrained performance,early strength,hydration heat,electrical resistivity,chemical shrinkage of KH3.Preferential adsorption and low-cost polycarboxylate superplasticizer:(1) Low-cost organic compounds preferentially adsorb on the surface of cement particles to shield active hydrating points.In this way,dispersibility and holding dispersibility have been enhanced.The cement with KH-d has good fluidity and holding fluidity and mechanical properties,but the cost is lower than naphthalene superplasticizer.(2) With increasing addition of hydroxy carboxylate,initial dispersibility increase.Hydroxy carboxylate restrain the hydration of C₃S,but accelerate the hydration C₃A and formation of AFt.With sulfonation-polyol,holding dispersibility of polycarboxylate superplasticizer increases.Sulfonation-polyol restrains hydration of C₃S,C₃A and formation of AFt. (3) In system of hydroxy carboxylate,sulfonation-polyol and polycarboxylate superplasticizer, initial dispersibility increases and holding dispersibility reduces with addition of hydroxy carboxylate.And compressive strength also reduces at 3d,7d and 28d.Initial dispersibility has little change and holding dispersibility increases with addition of sulfonation-polyol. There is little loss of fluidity for 1h with addition of 0.3%,but compressive strength of 3d and 7d reduces and strength of 28d doesn't drop.When addition of hydroxy carboxylate is 0.04-0.1%and addition of sulfonation-polyol is 0.1-0.3%,polycarboxylate superplasticizer has good dispersibility,holding dispersibility and mechanical properties.4.Mechanism of water-reducer in cement hydrating process:(1) Restrains hydration of C₃S and accelerates hydration C₃A at 1d.The chemical shrinkage with Calcium lignosulfonate for 1d has little change with addition.For FDN and KH,the chemical shrinkage for 1d reduces with addition.Compared with calcium lignosulfonate and FDN,KH is advantage to reduce cracking sensitivity and prevent early-age cracking behavior.(2) Because of acceleration of Calcium lignosulfonate for C₃A,electrical resistivity change little with increase addition,but peak of hydration heat has been cut and delayed.For FDN and KH,ability to prevent hydration becomes strong in early age with increase addition.So peak of hydration heat has been cut and delayed.(3) Microanalysis shows:water-reducer restrains hydration of C₃S and formation of CH in early age.If there is a proper addition,restraint becomes weaker and weaker with time going. Calcium lignosulfonate restrains hydration of C₃S and formation of AFt.FDN restrain hydration of C₃S at 1d age,but accelerates hydration of C₃S of 7d and 28d and formation of CH.KH restrain hydration of C₃S of 1d and 7d,but it has little effect on later hydration.