Tensile strength of sands treated with microbially induced carbonate precipitation

2020 ◽  
Vol 57 (10) ◽  
pp. 1611-1616 ◽  
Author(s):  
Ashkan Nafisi ◽  
Douglas Mocelin ◽  
Brina M. Montoya ◽  
Shane Underwood
Keyword(s):  
Tensile Strength ◽  
Large Earthquake ◽  
Carbonate Precipitation ◽  
Direct Tension ◽  
Sem Images ◽  
Cemented Soil ◽  
Tension Tests ◽  
Deformational Behavior ◽  
Microbially Induced Carbonate Precipitation ◽  
Sand Type

During large earthquake events where bending moments within soil cements are induced, the tensile strength of cemented soil may govern the deformational behavior of improved ground. Several studies have been conducted to assess the tensile strength of artificially cemented sands that use Portland cement or gypsum; however, the tensile strength of microbially induced carbonate precipitation (MICP)-treated sands with various particle sizes measured through direct tension tests has not been evaluated. MICP is a biomediated improvement technique that binds soil particles through carbonate precipitation. In this study, the tensile strength of nine specimens were measured by conducting direct tension tests. Three types of sand (coarse, medium, and fine) were cemented to reach a heavy level of cementation (e.g., shear wave velocity of ∼900 m/s or higher). The results show that the tensile strength varies between 210 and 710 kPa depending on sand type and mass of carbonate. Unconfined compressive strength (UCS) tests were performed for each sand type to assess the ratio between tensile strength and UCS in MICP-treated sands. Scanning electron microscopy (SEM) images and surface energy measurements were used to determine the predominant failure mode at particle contacts under tensile loading condition.

scholarly journals The Influence of Loading Rate on Direct and Indirect Tensile Strengths: Laboratory and Numerical Methods

2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Jie Liu ◽  
Gangyuan Jiang ◽  
Taoying Liu ◽  
Qiao Liang
Keyword(s):  
Tensile Strength ◽  
Tensile Stress ◽  
Crack Propagation ◽  
Large Scale ◽  
Loading Rate ◽  
Peak Stress ◽  
Direct Tension ◽  
Tension Tests ◽  
Indirect Tension ◽  
Indirect Tensile

To investigate different responses of direct and indirect tensile strengths to loading rate, direct and indirect tension tests were performed on sandstone, rust stone, and granite specimens. Typical load curves indicate that a peak tensile stress frequently appears before the second peak stress, used to calculate the tensile strength in indirect tension tests. As expected, increase in the loading rate increases the tensile strength. In addition, the calculated tensile strengths of the indirect tension tests are frequently higher. Interestingly, the increase ratio of the tensile strength with the increase in the loading rate in indirect tension tests is higher. To verify the above results, crack propagation and stress evolution in direct and indirect tension tests were dynamically monitored using PFC 3D. For direct tension tests, specimens fail at the peak tension point, corresponding to the tensile strength. However, for indirect tension tests, minor cracks, composing of continuous microcracks, form before the peak stress and accompany with the decreased slope of the compression curve. At the peak point, tensile stresses significantly concentrate at the crack tips and further cause large-scale crack propagation. In addition, the initiation stress instead of the peak tensile stress is closer to the tensile strength, obtained from the direct tests for the same loading rate.

MECHANICAL STRENGTH OF SEALED-CURED NEAT CEMENT-PASTE

2015 ◽  
Vol 2 (1) ◽  
Author(s):  
S. Walker ◽  
W. Choi ◽  
M. Picornell ◽  
R. Mohan ◽  
S. Hamoush
Keyword(s):  
Tensile Strength ◽  
Compressive Strength ◽  
Cement Paste ◽  
Concrete Strength ◽  
Curing Time ◽  
Portland Cement Concrete ◽  
Direct Tension ◽  
Tension Tests ◽  
Water To Cement Ratio ◽  
Program Show

The strength of Portland cement concrete is dependent on the strength of the cement paste binding the aggregates together. An understanding of the cement paste is the first step to assess the concrete strength. To this end, a program for strength testing of cement paste was implemented for water to cement ratios of 0.35 and 0.40. The compressive strength was evaluated using two inch cubes and four inch diameter cylinders; while the tensile strength evaluation was based on flexure and direct tension tests. All the specimens were cured in the mold the first day, followed by curing in sealed vacuum bags for the remaining of the time. The total curing time ranged from three, seven, fourteen and twenty-eight days. Three replicate specimens were prepared, cured, and tested for each combination of water to cement ratio, type of specimen, and time of curing. The results of the testing program show that while the compressive strength increases for increasing curing time, the tensile strength shows a consistent decline. These results indicate that the sealed curing forced that further hydration caused “self-desiccation” of the CSH, inducing new cracks or extension of existing cracks that would be responsible for the loss of tensile strength.

scholarly journals The role of bacterial urease activity on the uniformity of carbonate precipitation profiles of bio-treated coarse sand specimens

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Charalampos Konstantinou ◽  
Yuze Wang ◽  
Giovanna Biscontin ◽  
Kenichi Soga
Keyword(s):  
Calcium Carbonate ◽  
Calcium Chloride ◽  
Urease Activity ◽  
Coarse Sand ◽  
Carbonate Precipitation ◽  
Population Densities ◽  
Carbonate Cements ◽  
Microbially Induced Carbonate Precipitation

AbstractProtocols for microbially induced carbonate precipitation (MICP) have been extensively studied in the literature to optimise the process with regard to the amount of injected chemicals, the ratio of urea to calcium chloride, the method of injection and injection intervals, and the population of the bacteria, usually using fine- to medium-grained poorly graded sands. This study assesses the effect of varying urease activities, which have not been studied systematically, and population densities of the bacteria on the uniformity of cementation in very coarse sands (considered poor candidates for treatment). A procedure for producing bacteria with the desired urease activities was developed and qPCR tests were conducted to measure the counts of the RNA of the Ure-C genes. Sand biocementaton experiments followed, showing that slower rates of MICP reactions promote more effective and uniform cementation. Lowering urease activity, in particular, results in progressively more uniformly cemented samples and it is proven to be effective enough when its value is less than 10 mmol/L/h. The work presented highlights the importance of urease activity in controlling the quality and quantity of calcium carbonate cements.

Watertightness, cracking resistance, and self-healing of asphalt concrete used as a water barrier in dams

2013 ◽  
Vol 50 (3) ◽  
pp. 275-287 ◽  
Author(s):  
Yingbo Zhang ◽  
Kaare Höeg ◽  
Weibiao Wang ◽  
Yue Zhu
Keyword(s):  
Asphalt Concrete ◽  
Leakage Rate ◽  
Strain Rates ◽  
Self Healing ◽  
Test Results ◽  
Direct Tension ◽  
Coefficient Of Permeability ◽  
Tension Tests ◽  
Laboratory Test Results ◽  
Cracked Specimens

The coefficient of permeability of hydraulic asphalt concrete is in the range 10−8–10−10 cm/s. Laboratory test results show that triaxial specimens in axial compression can undergo axial strains up to 18% without any significant increase in permeability until approaching the compressive strength. For temperatures between 5 and 20 °C and strain rates between 2 × 10−3%/s and 5 × 10−3%/s, conventional hydraulic asphalt concrete can tolerate 1%–3% tensile strains before cracking in direct tension tests and strains up to 3%–4% in bending. At 20 °C the tensile and bending strains at cracking are 2–4 times higher than those at 0 °C, and at −20 °C they are approximately 0.2% and 0.8%, respectively. Asphalt concrete possesses pronounced crack self-healing properties. In the experiments, the crack leakage rate dropped 1–4 orders of magnitude within a few hours and the cracked specimens regained 55% of the intact tensile strength after only 1 day of self-healing. In summary, the comprehensive series of laboratory tests documents that asphalt concrete has characteristics that make the material extremely well suited for use in impervious barriers in dams, and the test results reported herein can be of great use in barrier design.

Desert Aeolian Sand Cementation via Microbially Induced Carbonate Precipitation

IFCEE 2021 ◽  
2021 ◽  
Author(s):  
Xichen Xu ◽  
Hongtao Wang ◽  
Wenbin Lin ◽  
Xiaohui Cheng ◽  
Hongxian Guo
Keyword(s):  
Carbonate Precipitation ◽  
Aeolian Sand ◽  
Microbially Induced Carbonate Precipitation
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