The dissertation is devoted to the study of the influence of modifying additives and carbonate fillers on the properties of dry construction mixtures in aggressive environments. For the first time, using a salt fog chamber, the impact of an aggressive environment on the stability of a modified cement matrix with carbonate fillers, water-retaining reagents, and various types of polymer powders (RPP) was tested.
Studying the initial parameters of mixtures with carbonates, it was found that with a low content of limestone, the 28-day strength of cements increases, while when chalk is used, the grade strength of the mixtures is lower. X-ray analysis confirmed the similarity of chalk and limestone, which eliminates the possibility of the influence of additional inclusions on strength indicators.
By the nature of the action of methyl hydroxyethyl cellulose, the compressive strength of the mixtures decreases with an increase in both their content in the mixtures and the viscosity of the cellulose ethers themselves. Ethers of low and medium viscosity decrease in strength with a content of 0.75 wt. % additive, which is 40%, while the maximum reduction in strength for high-viscosity esters is 60%. Ethers of high viscosity increase the water absorption of mixtures when their content in the system is increased from 2% to 6%. Medium and low viscosity esters have less effect on strength, which in turn shows their greater effectiveness when used in cementitious mixtures.
Calcium formate and RPP at a low content in construction mixes reduce the strength of the mixes by 9-15%% compared to the control compositions. At the same time, the compression strength value for the obtained mixtures remains within the limits of 42.5-50 MPa. Already higher concentrations (from 3 to 5 wt.% of additives) reduce the strength of the mixtures. Because of this, it can be argued that during further hardening of the mixtures, the grade strength will remain within the limits of the values obtained on the 28th day of hardening, if there will be no destructive effect on the products.
For mixtures with a carbonate filler, it was determined that the seawater solution has the greatest aggressiveness. There is a significant loss of cement strength from 20 to 50% compared to samples stored in tap water. A demonstrable effect on the stability of samples with cement-limestone mixtures can be seen in samples with a carbonate component content of up to 30 - 40%. Loss of strength compared to control samples in this seawater environment is 6-10%.
Low-viscosity cellulose ethers at low concentrations demonstrate the ability to reduce the destructive effect of sulfate-ion environments on the stability of cement mixtures at the age of samples of 196 days. This is provided by the relative inertness of the formed polymer films in the matrix of the cement mixture. At low concentrations (0.25 wt. %) of MHEC, destruction processes are slowed down and an increase in the relative durability of the cement mixture by 5-10% is seeing. At 0.5 wt. % and more of the additives, a strong thickening of the mixture occurs, which leads to the formation of voids, thereby increasing the permeability of the aggressive environment and, accordingly, reducing the stability of the mixtures more strongly.
Calcium formate, as well as vinyl acetate/versatate (Neolith 4400), can act as anti-corrosion additives due to low losses in the strength of samples. Additive Neolith 6700 shows significant stability up to 5 wt. % additives in the mixture for 168 days of aging in aggressive environments. At the same time, the use of Neolith 4400 has a more positive effect on the mixture under the influence of an aggressive environment. Thus, with a long stay in a calcium-sulfate environment, with a mixture containing 1% and 5% of vinyl acetate/versatate, the strength loss is 4-10 MPa, while in the sodium sulfate solution there was an increase in strength by 2-6 MPa compared to the control cement mortar.
The structure of the mixtures was studied by the method of electron microscopy before and after tests in aggressive environments.
The influence of polymer additives under the direct action of an alkaline environment was studied by the method of IR spectroscopy.
Based on the received data, the mix of the complex additive "ANTICOR 1Var" was designed. The effectiveness of the developed additive consists in slowing down the processes of loss of strength during long-term stay of cement products in aggressive environments.
It has been proven that the use of a combination of additives with a filler leads to a reduction in the impact of an aggressive environment in the late operational period. At the same time, under the continuous exploitation of products made of cement binders, or the reduction of the effect of an aggressive environment on solutions, a partial restoration of the strength occurs. Based on the obtained results, a combined additive was developed and a draft technological regulation was developed
