Anti-dispersion is an important technical indicator to measure the quality of anti-dispersion agents. Hydroxypropyl Methylcellulose(HPMC) is a water-soluble polymer compound, also known as water-soluble resin or water-soluble polymer, which can increase the viscosity of mixed water by increasing the consistency of the mixture. It is a hydrophilic polymer substance that can form a solution or dispersion after dissolving in water.
It was found that with the increase of HPMC content, the anti-dispersion of fresh cement mortar is getting better and better.
In a pilot project based on HPMC’s underwater non-dispersive concrete admixture application, the design strength rating is C25. In the basic test, the amount of cement is 400kg, amount of composite silica fume mixture is 25kg, and the optimum content of Hydroxypropyl Methylcellulose(HPMC) is 0.6% of cement. The water-cement ratio is 0.42, the sand ratio is 40%, and the yield of naphthalene-based high-efficiency water reducer is 8 %. The average strength of concrete specimens is 28d, the air is 42.6MPa, the average strength of underwater concrete for 28d with water droplet height of 60mm is 36.4MPa, and the ratio of formed concrete to air forming strength is 84.8%, the effect is more remarkable.
Experiments show that:
(1) The addition of Hydroxypropyl Methylcellulose(HPMC) has a significant retarding effect on the mortar mixture. As the HPMC content increases, the mortar solidification time is prolonged. At the same HPMC dosage, the molding time is longer. This function is good for pumping underwater concrete.
(2) The fresh cement mortar mixed with hydroxypropyl methylcellulose has good cohesiveness and almost no bleeding.
(3) The addition of water reducing agent improves the water demand of the mortar, but it must be properly controlled. Otherwise, it may sometimes cause a decrease in the underwater dispersibility of fresh cement mortar.
(4) The structure of HPMC mixed with HPMC is not much different from that of HPMC. The structure and density of the cement slurry placed in water and air are not much different. The 28d specimen under water molding is slightly brittle. The main reason is that the addition of Hydroxypropyl Methylcellulose(HPMC) greatly reduces the loss and dispersion of cement during casting, while reducing the compactness of cement stone. The underwater non-dispersive effect is ensured in the project due to the minimization of the amount of HPMC.
(5) Mixing Hydroxypropyl Methylcellulose(HPMC) underwater non-dispersible concrete admixture to control the dosage is beneficial to strength. The pilot project shows that the cement concrete strength ratio is 84.8%, and the effect is obvious.