scholarly journals Chloride Ingress in Chemically Activated Calcined Clay-Based Cement

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Joseph Mwiti Marangu ◽  
Joseph Karanja Thiong’o ◽  
Jackson Muthengia Wachira
Keyword(s):  
Compressive Strength ◽  
Portland Cement ◽  
Ordinary Portland Cement ◽  
Strength Development ◽  
Chloride Ingress ◽  
Calcined Clay ◽  
Apparent Diffusion Coefficients ◽  
Apparent Diffusion ◽  
Lower Porosity ◽  
Lower Chloride

Chloride-laden environments pose serious durability concerns in cement based materials. This paper presents the findings of chloride ingress in chemically activated calcined Clay-Ordinary Portland Cement blended mortars. Results are also presented for compressive strength development and porosity tests. Sampled clays were incinerated at a temperature of 800°C for 4 hours. The resultant calcined clay was blended with Ordinary Portland Cement (OPC) at replacement level of 35% by mass of OPC to make test cement labeled PCC35. Mortar prisms measuring 40 mm × 40 mm × 160 mm were cast using PCC35 with 0.5 M Na2SO4 solution as a chemical activator instead of water. Compressive strength was determined at 28th day of curing. As a control, OPC, Portland Pozzolana Cement (PPC), and PCC35 were similarly investigated without use of activator. After the 28th day of curing, mortar specimens were subjected to accelerated chloride ingress, porosity, compressive strength tests, and chloride profiling. Subsequently, apparent diffusion coefficients (Dapp) were estimated from solutions to Fick’s second law of diffusion. Compressive strength increased after exposure to the chloride rich media in all cement categories. Chemically activated PCC35 exhibited higher compressive strength compared to nonactivated PCC35. However, chemically activated PCC35 had the least gain in compressive strength, lower porosity, and lower chloride ingress in terms of Dapp, compared to OPC, PPC, and nonactivated PCC35.

scholarly journals The Effect of Clay Pozzolana-Cement-Composite on the Strength Development of a Hydraulic Backfill

2018 ◽  
Vol 18 (1) ◽  
pp. 32-38
Author(s):  
S. N. Eshun ◽  
Solomon Senyo Robert Gidigasu ◽  
S. K. Y. Gawu
Keyword(s):  
Compressive Strength ◽  
Portland Cement ◽  
Unconfined Compressive Strength ◽  
Ordinary Portland Cement ◽  
Cement Content ◽  
Cylindrical Specimen ◽  
Cement Composite ◽  
Strength Development ◽  
Increased Risk ◽  
Economic Considerations

The study sought to investigate the potential application of clay pozzolana as a supplement for cement in hydraulic backfill, using classified tailings from AngloGold Ashanti, Obuasi Mine. The percentage of the Portland cement that could be substituted with the clay pozzolana to produce backfill with best strength was determined. 10%, 25%, 30%, 35% and 40% of the ordinary Portland cement were replaced with clay pozzolana and then mixed with tailings and water. The slurry produced was cast into cylindrical specimen of 50mm diameter by 120mm high and tested for compressive strength after curing for 7, 14, 21, 28 and 56 days. The results indicate that, clay pozzolana-cement composite has potential for application in hydraulic back fill production without increased risk to safety and dilution. It was noted that hydraulic backfill with 10%, 25%, 30% and 35% of the ordinary portland cement replaced with clay pozzolana had strengths greater than those obtained for ordinary portland cement alone. Ten percent (10%) pozzolana content gave the maximum strength followed by 25% pozzolana. It is recommended that for safety and economic considerations, the cement content should be replaced by 25% pozzolana in the production of backfills. Keywords: Hydraulic Backfill, Portland Cement, Clay Pozzolana, Unconfined Compressive Strength

scholarly journals Mechanical Properties of OPC - Geocement Concrete

2019 ◽  
Vol 8 (4) ◽  
pp. 3733-3736
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Portland Cement ◽  
Ordinary Portland Cement ◽  
External Heat ◽  
Partial Replacement ◽  
Strength Development ◽  
Strength Increase ◽  
Heat Curing ◽  
Compressive Strength Development

Nowadays geopolymer concretes are subjected to heat curing. A large amount of highly corrosive and the hygroscopic alkaline activators are nowadays generally utilized in producing geopolymer concretes. In this paper, hybrid Ordinary Portland Cement (OPC) and geopolymer mixes are developed. The mainly used activator id the Solid potassium carbonate at different percentage is used as 5% & 10% of the weight of geopolymeric materials and OPC was blended with geopolymeric materials in different proportions. By adding cement, improves all the geopolymer properties except workability. By Applying external heat, it plays an important role in gaining strength. Strength gained by the absence of external heat is achieved by using Portland cement as a partial replacement of geocement. The influence of OPC content on the compressive strength development is investigated, and the optimized amount of solid activator to be used in the mix is also investigated. It is observed that percentage of strength increase decreases from52.24% to 14.77% as the OPC content increased from 20% to 60%.

scholarly journals Strength development of cement-treated sand using different cement types cured at different temperatures

2018 ◽  
Vol 195 ◽  
pp. 01006
Author(s):  
Lanh Si Ho ◽  
Kenichiro Nakarai ◽  
Kenta Eguchi ◽  
Takashi Sasaki ◽  
Minoru Morioka
Keyword(s):  
Compressive Strength ◽  
Portland Cement ◽  
Ordinary Portland Cement ◽  
Cement Content ◽  
Bound Water ◽  
Pozzolanic Reaction ◽  
Strength Development ◽  
Different Temperatures ◽  
Early Strength

This study aimed to investigate the strength development of cement-treated sand using different cement types: ordinary Portland cement (OPC), high early strength Portland cement (HPC), and moderate heat Portland cement (MPC) cured at different temperatures. The cementtreated sand specimens were prepared with 8% of cement content and cured under sealed conditions at 20οC and 40οC, and mortar specimens were also prepared for reference. The results showed that the compressive strength of cement-treated sand increased in order of MPC, OPC, and HPC under high curing temperatures. It was interesting that the compressive strength of the specimens using HPC was much larger than that of the specimen using OPC and MPC under 20οC due to the larger amount of chemically bound water. Additionally, it was revealed that under high curing temperatures, the pozzolanic reaction was accelerated in the cement-treated sand; this may be caused by the high proportions of sand in the mixtures.

scholarly journals Chloride Ingress in Cement Mortars Exposed to Acidithiobacillus thiooxidans Bacteria

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Onesmus Mulwa Munyao ◽  
Joseph Karanja Thiong’o ◽  
Jackson Muthengia Wachira ◽  
Daniel Karanja Mutitu ◽  
Genson Murithi ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Cement Matrix ◽  
Acidithiobacillus Thiooxidans ◽  
Chloride Ingress ◽  
High Porosity ◽  
Percentage Decrease ◽  
Apparent Diffusion Coefficients ◽  
Cement Mortars ◽  
Apparent Diffusion ◽  
Structural Failures

Concrete structures placed in aggressive aqueous environments are vulnerable to degradation. Majority of studies have linked structural failures to the ingress of deleterious ions into the cement matrix. Some microbial activities may accelerate the penetration of harmful materials into the cement matrix and hence cause pronounced deterioration. This work reports a laboratory-simulated study carried out to determine the extent of chloride ingress in cement mortars exposed to Acidithiobacillus thiooxidans. Test prisms were cast from Portland pozzolana cement (PPC) and ordinary Portland cement (OPC) with water-to-cement ratio maintained at 0.5. Acidithiobacillus thiooxidans bacterial solution of concentration 1.0 × 10 7  cell/mL was used to prepare microbial mortar prisms, whereas distilled water was used to prepare the control mortar prisms. The test prisms were subjected to porosity and accelerated chloride ingress after 28th day of curing. Compressive strength was determined after the 2nd, 7th, 28th, and 56th days of curing. Apparent diffusion coefficients (Dapp) were estimated from the solutions to Fick’s second law of diffusion. After the 56th day of curing, the microbial-treated mortars exhibited a significant reduction in compressive strength. The resultant percentage decrease in compressive strength was 30.74% and 19.88% for OPC and PPC, respectively. Further, microbial-treated mortars demonstrated both high porosity and chloride ingress as compared to the control test mortars. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses showed the formation of new deleterious products in the microbial-exposed mortars.

scholarly journals Biocementation Influence on Flexural Strength and Chloride Ingress by Lysinibacillus sphaericus and Bacillus megaterium in Mortar Structures

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Daniel Karanja Mutitu ◽  
Jackson Muthengia Wachira ◽  
Romano Mwirichia ◽  
Joseph Karanja Thiong’o ◽  
Onesmus Mulwa Munyao ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Flexural Strength ◽  
Apparent Diffusion Coefficient ◽  
Portland Cement ◽  
Bacillus Megaterium ◽  
Ordinary Portland Cement ◽  
Chloride Ingress ◽  
Strength Gain ◽  
Lysinibacillus Sphaericus ◽  
Apparent Diffusion

The concrete/mortar durability performance depends mainly on the environmental conditions, the microstructures, and its chemistry. Cement structures are subject to deterioration by the ingress of aggressive media. This study focused on the effects of Bacillus megaterium and Lysinibacillus sphaericus on flexural strength and chloride ingress in mortar prisms. Microbial solutions with a concentration of 1.0 × 107 cells/ml were mixed with ordinary Portland cement (OPC 42.5 N) to make mortar prisms at a water/cement ratio of 0.5. Four mortar categories were obtained from each bacterium based on mix and curing solution. Mortar prisms of 160 mm × 40 mm × 40 mm were used in this study. Flexural strength across all mortar categories was determined at the 14th, 28th, and 56th day of curing. Mortars prepared and cured using bacterial solution across all curing ages exhibited the highest flexural strength as well as the highest percent flexural strength gain. Lysinibacillus sphaericus mortars across all mortar categories showed higher flexural strength and percent flexural strength gain than Bacillus megaterium mortars. The highest percent flexural strength gain of 33.3% and 37.0% was exhibited by the 28th and 56th day of curing, respectively. The mortars were subjected to laboratory prepared 3.5% by mass of sodium chloride solution under the accelerated ion migration test method for thirty-six hours using a 12 V Direct Current power source after their 28th day of curing. After subjecting the mortar cubes to Cl media, their core powder was analyzed for Cl content. From these results, the apparent diffusion coefficient, Dapp, was approximated from solutions to Fick’s 2nd Law using the error function. Bacillus megaterium mortars across all mortar categories showed lower apparent diffusion coefficient values with the lowest being 2.6456 × 10–10 while the highest value for Lysinibacillus sphaericus mortars was 2.8005 × 10–10. Both of the test bacteria lowered the ordinary Portland cement Cl-ingress but Bacillus megaterium was significantly more effective than Lysinibacillus sphaericus in inhibition.

scholarly journals Performance of Ground Clay Brick Mortars in Simulated Chloride and Sulphate Media

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Festus Ngui Musyimi ◽  
Jackson Muthengia Wachira ◽  
Joseph Karanja Thiong’o ◽  
Joseph Mwiti Marangu
Keyword(s):  
Compressive Strength ◽  
Diffusion Coefficients ◽  
Blended Cement ◽  
Strength Analysis ◽  
Strength Development ◽  
Calcined Clay ◽  
Apparent Diffusion Coefficients ◽  
Clay Bricks ◽  
Sulphate Media ◽  
Experimental Findings

The durability of cement-based structures majorly depends on their resistivity to the aggressive media in the construction environment. The most aggressive ions commonly encountered in construction environment are chloride (Cl−) and sulphate (SO42−). The interactions of these ions with hydrated cement influence their durability and ultimate service life. This paper reports the experimental findings on an investigation on the diffusivity of Cl− and SO42− ions into mortars made from two mixtures: one made from ground calcined clay bricks (GB) and commercial ordinary Portland cement (OPC) and the other consisting of GB and Portland pozzolana cement (PPC). The test media were 3.5% Cl− and 1.75% SO42− solutions. For comparison, commercial OPC and PPC were also investigated. GB was blended with OPC at replacement levels of 25, 35, 45, and 50% to make OPCGB. Similar blends were also made with PPC replacement levels of 15, 20, and 25% to make PPCGB. Mortar prisms measuring 160 mm × 40 mm × 40 mm were cast at the water-to-cement ratios (w/c) of 0.40, 0.50, and 0.60 using each category of cement and cured in water for 3, 7, and 28 days. Compressive strength measurements were taken at each of the curing ages. The 28-day cured mortar prisms were subjected to compressive strength analysis and accelerated Cl− and SO42− ingress for 36 hours at 12 V. Ion profiling was done on the mortars, and diffusion coefficients of the Cl− and SO42− ions were approximated. The results showed that there was an increase in compressive strength after exposure to Cl− and SO42− ions. In addition, the ingress of Cl− and SO42− ions decreased with an increase in depth of cover. Blended cement exhibited lower Cl− and SO42− ingress than OPC. The ingress of Cl− was observed to be higher than that of SO42− ions. The ingress of Cl− and SO42− ions increased with an increase in w/c ratio. The results further showed that there was a drop in the ingress of Cl− and SO42− ions with an increase in replacement up to 35 percent for OPC. A 15 percent replacement showed a better compressive strength development compared with 20 and 25 percent replacement for PPC. Blended cement showed lower apparent diffusion coefficients (Dapp) compared with OPC. PPC, OPCGB-35, and PPCGB-15 exhibited similar performance in terms of strength development, aggressive ions ingress, and Dapp. In conclusion, it was found that the test cements, PPCGB-15 and OPCGB-35, can be used in similar tested environments as commercial PPC.

scholarly journals The potential use of pumice in mine backfill

2020 ◽  
Vol 1 ◽  
Author(s):  
Mohammed A. Hefni
Keyword(s):  
Compressive Strength ◽  
Portland Cement ◽  
Mining Industry ◽  
Strength Development ◽  
Natural Pozzolan ◽  
Mine Backfill ◽  
Natural Pozzolans ◽  
Cemented Backfill ◽  
Compressive Strength Development ◽  
Potential Use

Abstract The use of natural pozzolans in concrete applications is gaining more attention because of the associated environmental, economic, and technical benefits. In this study, reference cemented mine backfill samples were prepared using Portland cement, and experimental samples were prepared by partially replacing Portland cement with 10 or 20 wt.% fly ash as a byproduct (artificial) pozzolan or pumice as a natural pozzolan. Samples were cured for 7, 14, and 28 days to investigate uniaxial compressive strength development. Backfill samples containing 10 wt.% pumice had almost a similar compressive strength as reference samples. There is strong potential for pumice to be used in cemented backfill to minimize costs, improve backfill properties, and promote the sustainability of the mining industry.

Study on Waterproof and Water-Resistant Properties of Gypsum

2012 ◽  
Vol 476-478 ◽  
pp. 1585-1588
Author(s):  
Hong Pan ◽  
Guo Zhong Li
Keyword(s):  
Compressive Strength ◽  
Flexural Strength ◽  
Portland Cement ◽  
Water Absorption ◽  
Ordinary Portland Cement ◽  
Experimental Results ◽  
Softening Coefficient

The comprehensively modified effect of cement, VAE emulsion and self-made acrylic varnish on mechanical and water-resistant properties of gypsum sample was investigated and microstructure of gypsum sample was analyzed. Experimental results exhibit that absolutely dry flexural strength, absolutely dry compressive strength, water absorption and softening coefficient of gypsum specimen with admixture of 10% ordinary Portland cement and 6% VAE emulsion and acrylic varnish coated on its surface can respectively reach to 5.11MPa , 10.49 MPa, 8.32% and 0.63, respectively.

scholarly journals Strength Development and Elemental Distribution of Dolomite/Fly Ash Geopolymer Composite under Elevated Temperature

Materials ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 1015 ◽  
Author(s):  
Emy Aizat Azimi ◽  
Mohd Mustafa Al Bakri Abdullah ◽  
Petrica Vizureanu ◽  
Mohd Arif Anuar Mohd Salleh ◽  
Andrei Victor Sandu ◽  
...  
Keyword(s):  
Elevated Temperature ◽  
Fly Ash ◽  
Portland Cement ◽  
Ordinary Portland Cement ◽  
Raw Materials ◽  
Liquid Sodium ◽  
Strength Development ◽  
Elemental Distribution ◽  
Distribution Analysis ◽  
Geopolymer Composites

A geopolymer has been reckoned as a rising technology with huge potential for application across the globe. Dolomite refers to a material that can be used raw in producing geopolymers. Nevertheless, dolomite has slow strength development due to its low reactivity as a geopolymer. In this study, dolomite/fly ash (DFA) geopolymer composites were produced with dolomite, fly ash, sodium hydroxide, and liquid sodium silicate. A compression test was carried out on DFA geopolymers to determine the strength of the composite, while a synchrotron Micro-Xray Fluorescence (Micro-XRF) test was performed to assess the elemental distribution in the geopolymer composite. The temperature applied in this study generated promising properties of DFA geopolymers, especially in strength, which displayed increments up to 74.48 MPa as the optimum value. Heat seemed to enhance the strength development of DFA geopolymer composites. The elemental distribution analysis revealed exceptional outcomes for the composites, particularly exposure up to 400 °C, which signified the homogeneity of the DFA composites. Temperatures exceeding 400 °C accelerated the strength development, thus increasing the strength of the DFA composites. This appears to be unique because the strength of ordinary Portland Cement (OPC) and other geopolymers composed of other raw materials is typically either maintained or decreases due to increased heat.

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