The influence of soluble salts in water and soil salinity on the formation of cracks in concrete channels

Abstract

The Republic of Karakalpakstan in Uzbekistan characterized by a sharply continental climate and precipitation of less than 150 mm per year, saline soils and groundwater with high salt concentrations are widely distributed. The situation is exacerbated by the drying up of the Aral Sea and the appearance of salt aerosols in the region. The Bustan Canal is located in this area and is intended for irrigating 100,000 hectares of farmland. The reconstruction of the canal allows for the abandonment of mechanical irrigation and the transition of the system to gravity irrigation. After the canal was put into operation, longitudinal cracks appeared at three stations: 47+20, 202+80, and 218+00. To identify the causes, concealed work was carried out at these locations where cracks appeared. Laboratory analysis of water and soil was conducted to examine the concrete strength, soil particle size distribution, and free swell index. This article presents the results of water analysis for concrete and its maintenance, as well as chemical analysis of the soil. All analyses were performed in licensed laboratories following the relevant national standards. Water for moistening the soil to optimal moisture during embankment construction, for concrete, and for concrete maintenance was sourced from two wells drilled at PK 183+20 and PK 218+45. The analysis showed that the pH of the water was between 4 and 12.5, with a value of 8.2. The sulfate ions (SO4) were 845.54 mg/L, below the limit of 2700 mg/L; chloride ions were 222.7 mg/L, below the limit of 4500 mg/L; suspended particles were 800 mg/L, exceeding the norm of 300 mg/L. The total content of sodium ions (Na+) and potassium ions (K+) was 319.47 mg/L, below the norm of 1500 mg/L. The water from the wells did not contain films of petroleum products, oils, fats, or coloring impurities. Overall, the water was suitable for concrete and concrete maintenance. Further compression strength tests on the concrete showed that the design strength of V 15 (M200) was achieved. The chemical analysis of the soil was conducted using the water and salt-acid extraction method. The sum of the percentage contents of the main ions ranged from 0.159% to 0.289%, indicating a low degree of overall salinity. The content of sulfate ions reached 37.5 eq.%, and sodium and potassium cations reached 41.951 eq.%. The gypsum content was 1.185%, which is below the norm of 5%. The soil was not gypsumized and was sulfide-stable. The soil pH was within the normal range, at pH = 7.4 ± 7.6.