Onesmus Munyao

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 t...

Grinding aids (GAs) are polar chemicals introduced in cement mills in either liquid or powder form to improve on mill grindability efficiency. Studies have shown that some GAs not only help in grinding efficiency but also play vital roles in improving the product particle size distribution, product ability to flow in the mill, grinding energy reduction, and improvement on the separator efficiency. This review investigated the impacts of the GAs on the performance of some properties of cement when used as either mortar and/or concrete. The influence of the GAs incorporation in cement grinding on properties such as workability and setting times of the placed concrete and/or mortar has been covered in this review. The performance of GAs on ordinary portland cement (OPC) and blended cements with other supplementary cementitious materials such as pozzolana, fly ash, and slag has also been discussed. This is in view to tapping the maximum benefits of using GAs in cement production and use...

This paper reports study findings on the use of Lysinibacillus sphaericus (at 1.0 × 107 cells/ml concentration) to enhance and improve the physicomechanical and chemical properties of blended Ordinary Portland Cement (OPC). Blending was done separately with pulverized fly ash (PFA) and natural pozzolana (volcanic tuff) at substitution levels of 10%, 20%, 30%, 40%, 50%, 60%, and 70%. Mortar prisms of dimensions 40 mm by 40 mm by 160 mm were prepared and cured for the 2nd, 7th, 28th, 56th, and 90th days using Lysinibacillus sphaericus solution as mixing water and curing media. Commercial OPC and PPC mortar prisms cast and cured using distilled water were used as controls. Results showed that prisms treated with bacteria exhibited the highest performance on compressive strength development. Further microstructure analysis of blended cement incorporated with Lysinibacillus sphaericus bacteria showed significant amounts of reacted secondary cementitious materials compared to samples with...

This study investigated the pozzolanicity and compressive strength of mortar made from a mixture of ground calcined clay bricks (GB)vis-a-vis OPC and PPC from Kibwezi region-Kenya. The GB was subjected topozzolanicity tests and blended with OPC at replacement levels of 25, 35, 45 and 50 percent to make OPCGB. Similar blends were also made with PPC but at lower replacement levels of 15, 20 and 25 to make PPCGB.Water to cement ratios of 0.4, 0.5 and 0.6 were used to make mortar prisms.Three mortar prisms were prepared for each category of cement. The mortar prisms were subjected tocompressive strength analysis. The results showed a decrease in compressive strength with increase in replacement of OPC and PPC on 3 rd , 7 th and 28 th day of curing. 15 percent replacement showed a better compressive strength development compared to 20 and 25 percent replacement for PPC. PPC, OPCGB-35 and PPCGB-15 exhibited similar performance in terms of strength development. The test cements, PPCGB-15 a...

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  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...

Mixing water is very vital for development of concrete and/or mortar. It can also be a source of aggressive ions in the cured concrete/mortar. The study will investigate the effect of mixing water on performance of mortar made from selected Ordinary Portland Cement (OPC) and Portland Pozzolana Cement (PPC). Cement from three different companies will be used while mixing water will be sampled from five different localities with potential aggressive ions to cement mortar or concrete. The localities to be selected for water sampling will be areas with either CI-, S042-, Mg2+, alkalis or with high salt levels. The water samples will include borehole water, industrial waste water, runoff water, and river water. Cement mortar will be made using the sampled water vis a vis tap and distilled water and cured in accordance to Kenya Standard KS EAS 18: 2008. Compressive strength will be determined at 2nd, 7th, 28th and 90th day of curing. Setting time, soundness, pozzolanic activity, pore wate...

Cement-based materials are subject to degradation during their service life. Most of the structural failures have been associated with corrosion of the rebar due to chloride ingress, alkali aggregate reaction, and/or sulfate attack. Microbial activities, especially in waste water collection points such as sewer lines, may compromise the integrity of concrete structures. This study reports an experimental work carried out to determine the effect of Starkeya novella bacteria species on mechanical and microstructural properties of cement mortars. Mortar prisms were prepared from selected ordinary Portland cement (OPC) and Portland pozzolana cement (PPC) in Kenyan markets. Bacterial solution of 1.0 × 107 cell/mL concentration was used as either mix water, curing media, or both. Distilled water was used to prepare mortar prisms for control samples. Compressive strength was determined after the 7th, 28th, 56th, and 90th day of curing. Scanning electron microscopy (SEM) was tested on both ...

This study investigated the compressive strength performance of partially replaced Ordinary Portland cement with ground granulated blast furnace slag (GGBFS). The replacement was done at 5%, 10%, and 15 % GGBFS. A blank OPC was used as a control. Mortar prisms were prepared and cured with accordance to KS EAS 18:1-2001. The resultant compressive strength was determined at 2 nd , 7 th , 14 th and 28 th daysof curing.Chemical composition of GGBFS and the setting times of the resultant cement was also determined. Results obtained showed that the compressive strength increased significantly at 10% and 15% GGBFS replacement at 28 days of curing. GGBFS can thus be used as a suitable additive in partial replacement of OPC.

This study investigated the pozzolanicity and compressive strength of mortar made from a mixture of ground calcined clay bricks (GB)vis-a-vis OPC and PPC from Kibwezi region-Kenya. The GB was subjected topozzolanicity tests and blended with OPC at replacement levels of 25, 35, 45 and 50 percent to make OPCGB. Similar blends were also made with PPC but at lower replacement levels of 15, 20 and 25 to make PPCGB.Water to cement ratios of 0.4, 0.5 and 0.6 were used to make mortar prisms.Three mortar prisms were prepared for each category of cement. The mortar prisms were subjected tocompressive strength analysis. The results showed a decrease in compressive strength with increase in replacement of OPC and PPC on 3 rd , 7 th and 28 th day of curing. 15 percent replacement showed a better compressive strength development compared to 20 and 25 percent replacement for PPC. PPC, OPCGB-35 and PPCGB-15 exhibited similar performance in terms of strength development. The test cements, PPCGB-15 and OPCGB-35 can thus be used in building similar structures as commercial PPC.

The effect of sulphate ions in mixing water on performance of cement mortar was investigated. Mortar prisms were made using selected Portland Pozzolana cement and Ordinary Portland cement with sewage, swampy and borehole waters, commonly used as mix waters in most peri-urban set up in Kenya. Potable tap water was used as a control. Compressive strength was determined at 2 nd , 7 th , 28 th , and 90 th day of curing. Setting time was also investigated. Results showed that sewage and swampy mix waters had significant sulphate content. The sulphate ions reduced the early compressive strength development of cement mortar in both PPC and OPC. Further, sulphate ions retarded both initial and final setting times in PPC and OPC. The use of sewage and swampy waters as mix water containing high sulphate ions could lead to failure of concrete and/or mortar and hence building and construction.