Study On Modification And Chemical Mechanism Of Polycarboxylate Superplasticizers For Enhanced Clay Tolerance

In large size concrete project,a small amount of clay in sandstone materials will cause severe adsorption for polycarboxylate superplasticizers(PCE).Concrete community has been perplexed for so many years by this problem,which is usually called the adaptability problem of PCE.In this work,we have analyzed the layer crystal structure of montmorillonite and its adsorption law,a series of cationic compounds and nonionic compounds have been chosen as sacrificial agent,the competitive adsorption capacities of montmorillonite and PCE have been compared by rheologic property and its mechanism has been studied by using gel permeation chromatography(GPC),X-ray diffraction(XRD)and dynamic light scattering(DLS),on this basis,a series of novel sacrificial agents with excellent performance have been screened.The main research content is as follows:(1)Three new types of PCE with carboxylic and hydrophobic long branched chain end groups has been synthesized,its structure and performance have also been tested.Basing the interval size of montmorillonite,six kinds of cationic compounds with different molecular weights have been chosen.Investigating their competitive adsorption capacities and comparing them with PCE,two kinds of new sacrificial agents,polydimethyl diallyl ammonium chloride(PDADMAC)and crystal violet(CV),with great anti-clay performance have been screened.By using PDADMAC,the initial fluidity of PCE in the cement which contain montmorillonite has been increased from 230 mm to 241 mm,the passing flow loss rate has been decreased from 33.5% to 8.3%;and by using CV,the initial fluidity of PCE in the cement which contain montmorillonite has been increased from 230 mm to 259 mm,the passing flow loss rate has been decreased from 33.5% to 20.8%.The anti-clay mechanisms of these two sacrificial agents have also been investigated.(2)Basing the adsorption law of montmorillonite,we have chosen 8 kinds of nonionic compounds with different molecular weights.Investigating their competitive adsorption capacities and comparing them with PCE,three kinds of new sacrificial agents,high carbon fatty alcohol polyoxyethylene ether(AEO),polyethylene glycol(PEG)and D-sorbitol,with great performance have been screened.By using AEO,the initial fluidity of PCE in the cement which contain montmorillonite has been increased from 230 mm to 250 mm,the passing flow loss rate has been decreased from 33.5% to 16.0%;by using PEG-1500,the initial fluidity of PCE in the cement which contain montmorillonite has been increased from 230 mm to 274 mm,the passing flow loss rate has been decreased from 33.5% to 25.9%;by using D-sorbitol,the initial fluidity of PCE in the cement which contain montmorillonite has been increased from 230 mm to 256 mm,the passing flow loss rate has not been influenced.The anti-clay mechanisms of these three sacrificial agents have also been investigated.(3)Four kinds of structure-modified sacrificial agents have been synthesized by molecular geometry optimization,its structure and performance have been tested.Among these,urea iron owns better anti-clay performance than polyferric sulfate and ferric sodium gluconate,by using urea iron,the passing flow loss rate of PCE in the cement which contain montmorillonite has been decreased from 33.5% to 21.9%;the anti-clay performances of urea resin oligomer and cationic starch are the same,which can all make the initial fluidity of PCE in the cement which contain montmorillonite increasing from 230 mm to 244 mm and the passing flow loss rate decreasing from 33.5% to about 27.9%.Structure-modified sacrificial agent can make the molecule configuration of PCE in cement paste more stretch,which is beneficial for the decreasing of PCE absorption in montmorillonite.