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Properties of Locally Available River Dredged Soil Stabilized with Cement

MB Hossain
Department of Farm Structure and Environmental Engineering, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

Z Barman
Department of Farm Structure and Environmental Engineering, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

M Dey
Department of Farm Structure and Environmental Engineering, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

Abstract/ Executive Summary:

In Bangladesh, the topsoil of agricultural land is being used to manufacture burnt clay bricks for a long time. This is one of the major reasons for reducing the cultivable land every year. But, we have a huge amount of River Dredged Soil (RDS) available that could be used for manufacturing building materials as an alternate to the conventional bricks. In this regard, the present study has been performed to investigate various properties of RDS from the Brahmaputra River and different mixes of RDS containing different percentages of cement content. The physical properties such as specific gravity, unit weight, mean diameter, maximum dry density, and optimum moisture content of RDS were determined following standard procedures. Cylindrical specimens of RDS were prepared by mixing with different amounts of cement content. All the specimens were cured for 7, 14, and 28 days before testing. Water absorption of the RDS-cement specimens after 28 days was found between 14 to 18% which is in the range of first-class burnt clay brick. It was found that the water absorption decreases with the increase in the percentages of cement content. The unconfined compressive strength was observed to increase with the increment of cement content as well as curing age. The maximum unconfined strength was recorded for the specimens containing 14% cement and the rate of strength increment was about 45% in two weeks. It means the addition of cement with RDS will definitely increase the strength. But, the maximum use of cement must be decided based on the required strength and economic consideration. The deformation at failure was found to decrease with the increase in cement content. This indicates that the stiffness of the stabilized RDS would increase upon the increment of cement content. Based on the above test results, it is concluded that the dredged soil from Brahmaputra River can be stabilized with cement for making compressed earth block which would be an alternative to the burnt clay brick that uses valued agricultural soil as raw material.

Keywords: River dredged soil, Cement stabilization, Soil-cement, Compressed stabilized earth block, Unconfined compressive strength

Location: Farm Structure and Environmental Engineering of Bangladesh Agricultural University.

Start Date:

End Date:

Program Area: Resource Development and Management

Commodity: Land erosion

Objectives:

1. To evaluate the properties of river dredged soil collected from Brahmaputra River and

2. To prepare four different cement stabilized RDS specimens and assess their physical and mechanical characteristics.

Methodology:

The experimental program was carried out in two parts. First, the physical properties of the RDS were determined; then, the strength and physical properties of RDS with different cement content were investigated following a discussion on the test results. All the experimental programs were carried out at the Material Testing Lab and Soil Mechanics Lab in the department of Farm Structure and Environmental Engineering of Bangladesh Agricultural University. Material collection and preparation: Dredging is a displacement of soil carried out underwater. During the dredging of the river bed sludge of the Brahmaputra River, the soil was collected from Char Nilakshima, Mymensingh Sadar. The dredged soil was transported directly to the Material testing laboratory of the Bangladesh Agricultural University. As the soil was partially wet, it was air-dried spreading over a large tray until constant moisture content was achieved. The soil was then sieved through a 4.76 mm sieve. Tests of physical properties of RDS: The physical properties such as moisture content, unit weight, specific gravity, sieve analysis were determined in the Laboratory. The sieve analysis of the RDS was performed according to ASTM D422 standard test method. The specific gravity of the RDS was determined by the Pycnometer method. For soil to be used for bearing load, the compaction characteristic is important to know the maximum dry density and its corresponding moisture content. The compaction (standard proctor) test was performed according to ASTM D698 to know the highest density and optimum moisture content of the RDS. Preparation of cylindrical specimens: Four different mixes of RDS with cement were prepared for making cylindrical specimens. The cement content of four different percentages (4%, 8%, 12%, and 14%) was added to the RDS by weight. The RDS-cement admixtures were mixed with water according to the optimum moisture content of the soil obtained from the compaction test. The optimum moisture content of the RDS was found at about 19%. The soil-cement admixtures were mixed thoroughly using a motorized mixer machine. The cylindrical specimens were prepared in cast-iron molds of size 6” in height and 3” in diameter. Molds were first set up properly with the base of mold by a nut- bolt using a wrench for making cylindrical specimens. A total of 40 test cylinders were prepared. The average moisture content of the cylindrical specimens was calculated between 17% - 20% by the oven drying method. All the specimens were de-molded carefully. The cylinders after de-molding were kept on a polythene sheet and curing was done by sprinkling water using a sprayer. The curing period of specimens was up to 28 days. Test of unconfined compressive strength: Unconfined compression tests have been used in most of the experimental programs reported in the literature in order to evaluate the effectiveness of the stabilization with cement or to access the relevance of specific factors in influencing the strength of soil-cement admixtures. The unconfined compression tests were carried out up to failure, with the maximum load. Compressive strength is calculated by dividing the maximum load by the original loading surface area of a specimen in an unconfined compression test. The test method was followed according to ASTM D2166 standard. A displacement transducer with a data logger was attached to the compression testing machine to record the deformation of the cylindrical specimens at ultimate load. For testing unconfined compression strength, 3 nos. of each RDS-cement specimen were taken after 7, 14, and 28 days of curing by sprinkling water. Each test specimen was placed onto the flat surface of a circular pressure plate of the compression testing machine. The load was applied very slowly until the cylindrical specimen fails and the ultimate load for specimens was recorded.

Source of Information: Progressive Agriculture 32 (1): 71-77, 2020

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

In this study, various properties of locally available river dredged soil were investigated. The soil was then stabilized with four different percentages (4%, 8%, 12%, and 14%) of cement content. Finally, the cement stabilized RDS specimens were tested to determine their physical and strength properties. The key focus was to assess the suitability of cement stabilized RDS as an alternative raw material in the construction industry. Based on the test results, the conclusions obtained from this research work can be summarized as follows:

In the RDS, the sand content is found 72%, silt and clay fraction is 23% with 5% gravel. The sp. gr. was 2.63 and the mean particle size was 0.10 mm. The maximum dry density and optimum moisture content of the RDS were found at 1.71 gm/cm³ and 19% respectively.
The water absorption of RDS-cement specimens ranges from 14%-18% which was found decreasing with increasing cement content.
The highest average value of unconfined compressive strength was recorded as 3760kPa in the case of the specimens having a cement content of 14%. The highest strength increment was found nearly 45% from 14 days to 28 days of curing. The compressive strength was positively related to the percentage of cement content irrespective of curing periods.
An inverse relationship is observed between deformation and compressive strength of the stabilized RDS with the cement content. It has also been found that higher cement content in specimens reduced deformation at failure and changed soil behavior to a noticeable stiffness behavior.

Knowledge Management: Journal