The Improvement Of Additive To Clay Negative Effects On Polycarboxylate Superplasticizer

Different types of clay minerals show a completely different effect rule on the negative effect of polycarboxylate superplasticizer(PC) in relation to their physical and chemical properties. The influence rule of different clay on the performance of cement paste and mortar was studied,finding that montmorillonite which has greater adsorption capacity and expansion capacity has bigger negative effect on PC than illite and kaolinite. The true state of clay is composed of a variety of single mineral clay, so to study the negative effect of mineral composition on clay is particularly important.According to the impact mechanism of negative effect to PC by clay, this article confirmed PEG-4000、KCl and compound additives(PEG-4000:KCl=1:5) from the adsorbent and anti-expanders two aspects. Under different clay content, the effect rule of the effect of additives by the mineral composition of clay was studied by the change of the cement paste fluidity. At the same time, the MATLAB software was used to make regression analysis on the effects of the fluidity of cement paste improved by additive from clay mineral composition. And also to make them quantified that the clay’s negative effects and improving effect of additives by clay mineral composition. By studying the adsorbability and expansion performance between clay、additives and PC, the improvement methods and mechanism of the additives on the clay were expounded, which provides theoretical reference to practical work.The effect of clay’s mineral composition on the additives’ effect was discussed under different clay contents. The results show that when the dosage of clay is small, the initial loss time of each clay’s fluidity has extended from 60 min to 90 min, and the extent of improvement by additives to clay is small and different. The proportion of montmorillonite and illite in the mineral composition has little effect on additives’ effect. When the dosage of clay gets bigger, the proportion of montmorillonite and illite in the mineral composition would be bigger, and the improved effect of additives’ negative effects on clay can be more significan.According to the results of mortar flow test, the improving effect of 4% clay content is the most significant by compound additives, and usually there is no bleeding. Without additives each age of strength would reduce if the content of clay is bigger, among them the biggest decline of 3d strength gets to 36.6% under 6% clay content. In summary, the compounding additives bring some improvement to the mortar strength under various clay content. With 6% clay content, the most increasement of 3d strength gets to 26.9% by compound additives, which is much larger than 7d and 28 d.Compared with F2%, the negative effect coefficient of each clay increases 40% in F4%(regression equation with 4% clay content) without additives, the negative effect increasing range of MMT gets to 255.0% in F6%, while the increasing range of ilite and kaolinite have little change. The improved effect of negative effect of montmorillonite(MMT)by additives is the best under various clay content. Whereinto the negative effect of each clay reduces over 28% in F2%, and over 56% in F4%, and the negative effect of MMT reduces to 75% in F6%. The reduction of negative effect of MMT and ilite are obvious by additives, but it has little change for kaolinite.The effect of additives to adsorbability and interlayer spacings was tested by TOC test and XRD analysis and then the improved ways of adsorbability and expansion performance of clay mineral with aadditives have been discussed. The results show that, the additives has no effect on the change of adsorbing capacity and Zeta Potentiall between the cement and PC, and the additives are adsorbed priority than PC by MMT. The effect of the compound additive was best,6% compound additives would lead to that the adsorption capacity between the Na-MMT to PC declines to 65.0%. After adding 3% KCl,the change of MMT interlayer spacing is equivalent to the effect of 9% PEG-4000 content. When the content of KCl is 6% and 9%, the decline of its spacing is 10.3% and 14.8%, which is better than the improved effect of compound additives 8.5% and 11.9% under the same dosage. This is due to that the K+ would reduce the electric double layer in the additives, making the the potential on the surface of clay minerals reduced, thus reducing the adsorption and swelling between clay mineral and PC.