Properties Research Of Cellulose Ethers Modified Cement Pastes

This study comes from the National Natural Science Foundation of "Hydration process and microstructure formation mechanism of thin-layer cellulose ether modified mortar "(50902107). Content and viscosity of cellulose ether (MC) on cement paste properties are studied by workability, mechanical properties, cement hydration and microstructure analysis of cellulose ethers modified cement paste. Hydration law of cellulose ether modified cement paste is studied by properties of thin-layer cellulose ether modified cement pastes.The results are listed as follows:1. Content and viscosity of cellulose ether (MC) on the workability of cement paste are studied by water retention, water loss and setting time of cement paste modified cellulose ether.With the content of cellulose ether increasing, water retention and setting time of cement paste is enlarged and water loss of cement paste is decreased. When the content is 0.6%, water retention and water loss are respectively 99% and 1.1 g/mm2×10-4. Water retention and water loss does not change, when the content is beyond 0.6%. Under the same content, water retention and water loss of MC modified cement paste improve with the increasing of cellulose ether viscosity. When the content is 0.6%, the initial and final setting time of cement paste is respectively 425min and 575min.The initial and final setting time increases by 93% and 72%, compared with the blank sample (220min and 335min).2. Content and viscosity of cellulose ether (MC) on the mechanical properties of cement pastes are studied by compressive strength and tensile strength.(1) The compressive strength of hardened cement pastes continuously decrease, with the content of cellulose ether increasing. When content is less than 0.4%, the compressive strength of cement paste decrease with the content of cellulose ether increasing. When the content is more than 0.8%, compressive strength does not change. MC1, MC2 and MC3 can cut down the compressive strength of cement paste.MC2 and MC3 can significantly cut down the compressive strength of cement paste of 7 days and 28 days, while the MC1 can significantly cut down the compressive strength of cement paste of 3d.(2) The tensile bond strength between cement paste and mortar board:When the content is less than 0.7%, the tensile bond strength enlarge with the content of cellulose ether increasing. When the content is more than 0.7%, the 3 days tensile bond strength almost does not change, the 7 days tensile bond strength slowly increase and the 28 days tensile bond strength decrease. Under the same content, the tensile bond strength enlarges with the increasing of cellulose ether viscosity.The tensile bond strength between aerated concrete and cement paste:When the content of cellulose ether is less than 0.7%, the 3 days and 7 days tensile bond strength of cement paste enlarge as the content of cellulose ether increasing dramatically. When doped volume of cellulose ether is more than 0.7%, tensile bond strength increases slowly. When doped volume of cellulose ether is less than 0.4%, the 28 days tensile bond strength of cement paste enlarge as the doped volume of cellulose ether increasing dramatically. When the doped volume of cellulose ether is more than 0.4%, the tensile bond strength almost doesn't change.3. Hydration law and microstructure of the cellulose ether modified cement paste are analysised by using XRD, TG-DSC-DTG, FTIR, SEM, and hydration heat methods.(1) We fing that MC does not change the kinds of hydration products by XRD, DTG and FTIR analysis. Hydration products are Ca (OH) 2and ettringite. C-S-H gel, ettringite, Ca (OH)2 and other hydration products of blank cement pastes generate earlier than MC modified cement pastes. The shape of C-S-H gel tends to be more fibrous and ettringite becomes more slender. C-S-H gel and ettringite are throughout the cement particles, cross-linked with each other in blank cement pastes. C-S-H gel shows fine velvet-like and the size of ettringite is short in MC modified cement pastes. (2) MC significantly delayed the induction period and accelerated phase of cement hydration. The induction period of cement hydration enlarge, with the MC content increasing. Accelerated phase gradually moves backwards and the exothermic peak decreases.4. Law of thin (2mm,6mm and 10mm) cellulose ethers modified cement pastes was studied under rapidly water-loss conditions.Because of high water absorption (35%) of fired brick matrix, in the XRD diffraction patterns, only a small amount of Ca (OH) 2 was found of 2 mm thick cement pastes. A lot of C3S and C2S still don't hydrate after 7 days hydration. After 6 hours hydration, diffraction peaks of Ca (OH)2 and ettringite were found in the XRD patterns of 6 mm and 10 mm thick cement paste. Under the same age, from 2 mm to 10 mm thick cement pastes, the intensity of diffraction peak, exothermic peak and vibration peak of Ca (OH) 2 enhanced.