Study On The Synthesis And Properties Of Novel Polycarboxylate-Type High Range Water-Reducers

As polycarboxylic acid type water-reducers exhibit an excellent ability of water-reducing and prevention of slump loss, their development has been being widely paid attention to. In this dissertation, a series of macromers of polyethylene glycol unsaturated carboxylic esters and polycarboxylic water-reducers (Modified polycarboxylic water-reducers, abbreviated as MPC) had been developed and tested for properties. The high quality macromers bearing with polyoxyethylene groups (PEO) were produced by the esterification reaction of polyethylene glycol with the over-dosaged unsaturated carboxylic acid under a temperature of 80~130 ℃ in the absence of solvents by adding a specified amount of hydroquinone as the polymerization inhibitor and the low-oxidation catalyst of acidic or amine substance. The reaction process was controlled by measuring the acidic value of reactants and calculating the harvest ratio of polyethylene glycol's esterification. The further esterification of macromers was then restrained by quick cooling or adding a specified amount of the low carbon aliphatic alcohol. Through the molecule design, a series of novel polycarboxylic acid type water-reducers (MPCs) of various properties with a given structure were prepared by a copolymerization reaction under a certain temperature in a water solution system from the polyethylene glycol unsaturated carboxylic acid esters and other olefin monomers with persulfate salt as a radical initiator. The water-reducing ratio of the standard-type MPC-1 in concrete was 24.9% and that of the retarded-type MPC-2 was 22.8% at the same solid dosage of 0.45%. The slump of concretes with such MPCs were maintained without any loss for 1~2 hours. The properties of MPCs were obviously superior to those of the domestically produced conventional naphthalene-based water-reducers, and slightly inferior to those of the imported polycarboxylic acid type water-reducers as compared samples. The MPCs can be used to prepare high-volume fly ash high-flowing concrete, high-strength high performance concrete and high-durability concrete. It was found that, the PEO chain length and the quantity of macromers influenced the average molecular weight and it's distribution of copolymers of MPC, and thus determined the ability of MPC to disperse cement particles and maintain the flowability of concrete. Methllyl sulfonic acid acted as a chain transfer agent besides supplying the strong polar anionic sulfonic group. 2-acrylamido-2-methlpropanesufonic acid increased the dispersibility and the flow retainability of MPC simultaneously. Maleic anhydride could more greatly increase the dispersibility than acrylic acid could. Several other carboxylic derivatives could enhance the ability of MPC to maintain flow of concrete and its stability under storage. High performance MPC can be obtained through optimum design by the modification of its structure, such as the introduce of PEO block chains and side chains, long and short side chains, anionic and cationic groups, etc., and the compatibility of the water reducer with cement and its storage stability can also be improved.