Effect of complex chemical additives on the durability of hydraulic-engineering concrete

Abstract

Chemical additives are used in the manufacture of concrete and reinforced-concrete elements to accelerate hardening and to increase the density and durability of concrete. However, the presently used additives (CaCI2, Na2S04, NaF2, K2C03, Ca(N03)2, NaCI, etc.) along with their favorable properties also have shortcomings (possibility of corrosion of reinforcement, increase of concrete shrinkage, decrease of mix mobility, etc.). Studies have been carried out in the laboratory and the field to find chemical additives for accelerating concrete hardening and increasing its strength and impermeability to meet the requirements of durability imposed on structural elements of hydraulic structures. They should also be easy to use and inexpensive.As a result of concrete research, complex chemical additives of calcium chloride and ammonium nitrate, effectively influencing the rate of hardening, density, and impermeability, and additives increasing the density and impermeability (iron nitrate or sodium silicate in combination with the plasticizer sulfite waste liquor (SWL) or sulfite-yeast waste liquor (SYL)) were proposed. Selection of the accelerator was based on the fact that cheap and available compounds (CaCI= and NH~NO~ --effective accelerators) increase the density and strength of concrete. Furthermore, NH~NO3 does not corrode reinforcement.