Effect Of Acrylate On The Mechanical Performance And The Hydration Process Of Cement

Ordinary Portland cement as the indispensable bulk materials for infrastructures,occupies an important position in water conservancy, transportation, industrial facilities, civilconstruction and other major projects. However, the composition and the internal porestructure of cement lead to poor corrosion resistance, which will results in landslide damage,and bring abou more security problems and large amount economic losses. To solve thisproblem, our group use organic matter modification method to improve the corrosionresistance of Portland cement. Based upon the pre-trial, acrylate was shown to not onlyimprove pore structure of cement paste to improve the corrosion resistance, but also reinforcecement matrix to improve mechanical properties. However, the interaction between acrylateand cement, modification mechanism as well as the hydration process still needs furtherdiscussion and study.In experiment, the self-prepared acrylate was used as main agent, compounded withadditives （initiator, accelerator and crosslinking agent） which leads polymerization in thecement hydration progress, to improve cement properties. First, we studied the effects ofdifferent amount of acrylate acid and additives on the cement performance, and then find theoptimal amount of them. Second, Simulation and analysis the polymerization of acrylate inthe cement pore solution by means of infrared spectral （IR）. Last, according to testing resultsof heat of hydration, IR, DTA-TG, XRD and SEM, the paper emphatically studied the effectof acrylate acid on cement hydration process and on the morphology of hydration products.By studying the influence of calcium acrylate and additives on cement properties, wefind that calcium acrylate solution will affect the early strength of cement, but benefit fromthe long-term strength. When the calcium acrylate with amount of1.5%, the optimal dosageof the additives are:2%initiator,1.5%accelerator, and10%crosslinking agent, thecompressive strength of28day hydration increases by19.8%, and the sulphate corrosionresistance is much better, increases by5.1%than that of control sample.Learning from the testing result of compressive strength and corrosion resistance ofmagnesium acrylate modified cement, it performs not such better than calcium acrylate. Whenthe magnesium acrylate with amount of1.0%, and the additives with optimal dosage of3% initiator,0.5%accelerator, and10%crosslinking agent, the compressive strength for28dayincreases by10.7%, and the sulphate corrosion resistance increases by2.4%than that ofcontrol sample.In experiment, the saturated Ca（OH）₂solution was used to simply simulate the cementpore solution environment, with the methord of IR to verify the good polymerization ofacrylate in the cement pore solution. The study also found that calcium acrylate in alkalineenvironment can react with free Ca²⁺to form unstable complexes, and shorten thepolymerization time.The experimet using a variety of testig methord detailedly studied the effect of calciumacrylate on cement hydration process. It’s found that calcium acrylate has certain waterreducing effect and shorten the initial setting as well, the time for final setting initiallyincreases and then decreases with the amount of calcium acrylate. According to the testingresults of heat of hydration and IR, calcium acrylate promoted the early formation of AFt, anddue to its complexation with Ca²⁺, promoted the hydrolysis of C₃S which increases thehydration exothermic rate in C₃S hydration period. The DTA-TG and XRD analysis showsthat, calcium acrylate inhibited the transformation from AFt to AFm, and influence thenucleation and precipitation of Ca（OH）₂, which leads to less Ca（OH）₂generation for3h-24hhydration. Hydrate for3d-7d, the polymer film covers on the surface of cement particleaffected the calcium silicate hydration, as a result, the Ca（OH）₂formation, bound watercontent and hydration degree is lower than control samples and the strength is lower as well.In the later hydration period, calcium acrylate made cement paste more fully hydrated andwith higher strength, as a result of better dispersion of the cement paste and increase inconcentration of Ca²⁺in the liquid.It can be seen from the SEM photograph of calcium acrylate modified cement for7d,calcium acrylate affects the morphology of hydrated calcium silicate, which generated afibrous, overlapped C-S-H （II） crystals in the cement pore. In SEM images of28days’hydration, we find some smooth-surfaced, gelatinous polymer wrapped in the hydrationproducts, to form a close connection with the cement matrix, which will have a positive effectfor improving the cement structure and performance. The experiment also studied the effect of magnesium acrylate on cement hydrationprocess, and made a simple comparison with calcium acrylate. Magnesium acrylate also haswater reducing effect, and the influence to initial setting and final setting is similar to calciumacrylate. According to the results of heat of hydration and IR, magnesium acrylate alsopromoted the early formation of AFt, the difference is that magnesium acrylate reduced thehydration exothermic rate in induction period and C₃S hydration, which had significantlydelaying and inhibitory effect on early heat of hydration. The XRD analysis shows thatmagnesium acrylate promoted the formation of Ca（OH）₂in3-6hours’ hydration, but affectedthe hydration of calcium silicate and formation of Ca（OH）₂in the following3days, whichobviously delayed the hydration progress. Hydrate for3d-28d, magnesium acrylate promotedthe transformation from AFt to AFm, and ultimately promote the process of hydration.From the SEM photograph of magnesium acrylate modified cement for1day and3days,it can be seen some smooth-surfaced, gelatinous polymer wrapped in the surface of hydrationproducts, influenced the early hydration of cemen. In SEM images of3days’ hydration, alarge number of fibrous, overlapped C-S-H （II） crystals can be found growing in pores orloose region, which has a positive effect for improving the cement paste density and lowerporosity. In SEM photograph of28days’ hydration, the transformation from AFt to AFm bothappears in modified cement and control samples.