Influence of Starkeya novella on Mechanical and Microstructural Properties of Cement Mortars

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 bacterial and control mortar prisms after the 28th day of curing. Both PPC and OPC exhibited significant decrease in compressive strength for bacterial-prepared mortars as compared to controls. SEM analysis showed extreme erosion on the microstructure of the microbial mortars. This was denoted by massive formation of ettringite and gypsum which are injurious to mortar/concrete.

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Chloride Ingress in Cement Mortars Exposed to Acidithiobacillus thiooxidans Bacteria

Advances in Materials Science and Engineering ◽

10.1155/2020/4191806 ◽

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.

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Effects of Bacillus subtilis biocementation on the mechanical properties of mortars

Revista IBRACON de Estruturas e Materiais ◽

10.1590/s1983-41952019000100005 ◽

2019 ◽

Vol 12 (1) ◽

pp. 31-38 ◽

Cited By ~ 1

Author(s):

N. SCHWANTES-CEZARIO ◽

M. F. PORTO ◽

G. F. B. SANDOVAL ◽

G. F. N. NOGUEIRA ◽

A. F. COUTO ◽

...

Keyword(s):

Mechanical Properties ◽

Compressive Strength ◽

Calcium Carbonate ◽

Cementitious Materials ◽

Mechanical Analysis ◽

Sem Analysis ◽

Subtilis Strain ◽

Cement Mortars ◽

Water To Cement Ratio ◽

Mixing Water

Abstract This study aims to evaluate the influence of B. subtilis AP91 spores addition on the mechanical properties of mortars. B. subtilis strain AP91, isolated from rice leaves of the needle variety, which has an early cycle of production, was used at the concentration of 105 spores/mL in mortars with cement-to-sand ratio of 1:3 (by weight) and water-to-cement ratio (w/c) of 0.63. These spores were added in two different ways: in the mixing water and by immersion in a solution containing bacterial spores. Scanning Electron Microscope (SEM) analysis showed crystals with calcium peaks on the EDS, which possibly indicates the presence of bioprecipitated calcium carbonate. The results obtained in the mechanical analysis showed that the bioprecipitation of CaCO3 by B. subtilis strain AP91 was satisfactory, particularly when the spores were added in the mixing water, increasing the compressive strength up to 31%. Thus, it was concluded that the addition of B. subtilis AP91 spores in the mixing water of cement mortars induced biocementation, which increased the compressive strength. This bioprecipitation of calcium carbonate may very well have other advantageous consequences, such as the closure of pores and cracks in cementitious materials that could improve durability properties, although more research is still needed on this matter.

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Comparison of the influence of silica-rich supplementary cementitious materials on cement mortar composites: Mechanical and microstructural assessment

10.21203/rs.3.rs-157559/v1 ◽

2021 ◽

Author(s):

Ozer Sevim ◽

Cagrı Goktug Sengul

Keyword(s):

Compressive Strength ◽

Fly Ash ◽

Cement Mortar ◽

Bottom Ash ◽

Cementitious Materials ◽

Maximum Strength ◽

Supplementary Cementitious Materials ◽

Microstructural Properties ◽

Cement Production ◽

Mechanical And Microstructural Properties

Abstract The silica-rich supplementary cementitious materials (SCMs) are the key components of mechanical and microstructural properties. The use of SCMs results in improving the mechanical and microstructural properties and decreasing the environmental burden caused by cement production. In this regard, this paper reports a study to compare the influence of silica-rich supplementary cementitious materials (slag, fly ash, and bottom ash) having similar Blaine fineness on cement mortar composites in terms of mechanical and microstructural properties. First, supplementary cementitious materials (slag, fly ash, and bottom ash) were ground at similar cement Blaine fineness (~ 3300 cm2/g) and then by replacing 5% and 20% with cement, the 7-, 28-, 90-day mechanical and microstructural properties of cement mortar composites incorporating SCMs were examined. As a result, it was observed that the compressive strength and microstructural properties of cement mortar composites incorporating slag gave maximum strength and microstructural properties according to samples with fly ash and bottom ash having similar fineness and this will decrease the required amount of cement for the target properties by using slag, thus the number of CO2 emitted to nature will also decrease.

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Investigating the Effects of Polyaluminum Chloride on the Properties of Ordinary Portland Cement

Materials ◽

10.3390/ma12203290 ◽

2019 ◽

Vol 12 (20) ◽

pp. 3290

Author(s):

Taewan Kim ◽

Choonghyun Kang ◽

Sungnam Hong ◽

Ki-Young Seo

Keyword(s):

Compressive Strength ◽

Portland Cement ◽

Ordinary Portland Cement ◽

Chloride Ions ◽

Aluminum Silicate ◽

Microstructural Properties ◽

Sem Images ◽

Polyaluminum Chloride ◽

Friedel’S Salt ◽

Mechanical And Microstructural Properties

This study investigates the mechanical and microstructural properties of paste comprising ordinary Portland cement (OPC) added with polyaluminum chloride (PACl). The properties of the resulting mixture are analyzed using compressive strength, X-ray diffraction, scanning electron microscopy (SEM), mercury intrusion porosimetry, and thermogravimetric analysis. The results show that the addition of PACl improves the mechanical properties of OPC paste, that calcium-(aluminum)-silicate-hydrate (C-(A)-S-H) gel and Friedel’s salt are the major products forming from the reaction with the aluminum and chloride ions in PACl, and that the portlandite content decreases. Moreover, the size and number of micropores decrease, and compressive strength increases. All these phenomena are amplified by increasing PACl content. SEM images confirm these findings by revealing Friedel’s salt in the micropores. Thus, this work confirms that adding PACl to OPC results in a mixture with superior mechanical and microstructural properties.

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The role of delayed water curing in improving the mechanical and microstructural properties of alkali activated fly ash based geopolymer paste blended with slag

World Journal of Engineering ◽

10.1108/wje-03-2018-0103 ◽

2019 ◽

Vol 16 (1) ◽

pp. 103-114

Author(s):

Debabrata Dutta ◽

Somnath Ghosh

Keyword(s):

Fly Ash ◽

Base Material ◽

Rest Period ◽

High Rate ◽

Microstructural Properties ◽

Durability Test ◽

Content Type ◽

Water Curing ◽

Mechanical And Microstructural Properties ◽

Geopolymer Paste

Purpose This paper aims to investigate the effect of delayed water curing on the mechanical and microstructural properties of fly ash-based geopolymer paste-blended with Ground Granulated Blast Furnace Slag (GGBS) with different rest periods. Design/methodology/approach The blended geopolymer paste was composed of GGBS (15 per cent of the total weight) and the base material, Fly Ash (FA). The blended mix was activated by activator solution (Sodium hydroxide and Sodium silicate) containing 6 per cent Na2O of total base material. The effect of delayed water curing has been studied by gradually increasing the aging period (Rest Period) from 2 hours to 24 hours in the formation of activated outcome along with Calcium Silicate Hydrate (CSH). To analyze the mechanical and microstructural properties of the resultant blended geopolymer paste, compressive strength test, FESEM and XRD have been carried out. Moreover, a long-term durability test subjected to sulphate exposure has been performed to evaluate the durability of the designed sustainable geopolymer paste. Findings The present paper shows that the delayed water curing incorporates secondary heat input enhancing the partial polymer formation along with CSH. Slag-blended AAFA-based geopolymer paste is seen to exhibit quick setting property. Also, AAFA-based geopolymer paste samples subjected to longer rest period show early strength gain at a high rate under water curing as compared to those subjected to the shorter rest period. Originality/value To the best of authors’ knowledge, the effect of delayed water curing on the mechanical and microstructural properties of slag-blended AAFA-based geopolymer paste has not been studied before.

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Enhanced Mechanical and Microstructural Properties of Portland Cement Composites Modified with Submicron Metakaolin

Advances in Civil Engineering ◽

10.1155/2020/8882385 ◽

2020 ◽

Vol 2020 ◽

pp. 1-13

Author(s):

Yaoyu Wang ◽

Jiye Li ◽

Lihan Jiang ◽

Lihua Zhao

Keyword(s):

Compressive Strength ◽

Flexural Strength ◽

Portland Cement ◽

Pore Structure ◽

Hardened Cement ◽

Microstructural Properties ◽

Cement Slurry ◽

Curing Period ◽

Practical Engineering ◽

Mechanical And Microstructural Properties

This work aims to study the influence of submicron metakaolin (SMK) on the mechanical strength, pore structure, and microstructural properties of hardened cement-based slurry (HCS). Portland cement was replaced by SMK at a proportion of 1, 3, 5, and 7 wt%. The compressive strength and flexural strength of the HCS samples were tested at a curing period of 3, 7, 14, and 28 days, and the pore structure of the specimens was analyzed by mercury intrusion porosimetry (MIP) at a curing period of 3 and 28 days. The microstructure characteristics of the hardened samples were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Thermogravimetric analysis (TGA) was also employed to analyze the change in the chemical composition of the HCS. The results showed that the SMK could accelerate the hydration rate of the cement and could improve the mechanical properties of the HCS; the compressive strength and flexural strength of the HCS samples were remarkably enhanced, compared to those of the plain cement, by 67 and 46%, respectively, at a curing period of 3 days and by 33 and 35%, respectively, at a curing period of 28 days. The SMK had a significant impact on the internal pore structure of the hardened samples, and the number of pores with a diameter of larger than 3000 nm significantly decreased. Because the hydration products filled the pores, the microstructure of the HCS was further refined and densified with the addition of SMK. Submicron metakaolin has a simple process and high activity, which can significantly improve the performance of the cement slurry. Therefore, submicron metakaolin has the potential for practical engineering applications.

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Evaluating Micro-Structure, Hydration and Thermal Expansions of Cement Containing Nano-Silica

GIS Business ◽

10.26643/gis.v15i1.18226 ◽

2020 ◽

Vol 15 (1) ◽

pp. 158-165 ◽

Cited By ~ 1

Author(s):

Dr. Sarvesh PS Rajput

Keyword(s):

Portland Cement ◽

Mechanical Characteristics ◽

Microstructural Properties ◽

Nano Silica ◽

Micro Structure ◽

Microstructural Characteristics ◽

Mechanical And Microstructural Properties

This study reported that the addition of nano-silica enhances the mechanical characteristics of concrete as its compressive, flexural and tensile split strengths are increased. As a comparison mixture to equate it along with nano-modified concrete, ordinary samples of Portland cement (OPC) have been utilized. Herein, upto 6.0 percent of OPC has been substituted by nanosilica. In fact, the introduction of nanosilica improves mechanical and microstructural characteristics of concrete by significantly (28 to 35%). The finding therefore, indicated that partly replacing OPC with up to 5 percent nanosilica increases the mechanical and microstructural properties cured up to ninety days as opposed to the standard OPC mix.

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Incorporation of Iraqi Rocks in the Production of Eco-Friendly Cement Mortar

Engineering and Technology Journal ◽

10.30684/etj.v38i10a.1479 ◽

2020 ◽

Vol 38 (10A) ◽

pp. 1522-1530

Author(s):

Rawnaq S. Mahdi ◽

Aseel B. AL-Zubidi ◽

Hassan N. Hashim

Keyword(s):

Mechanical Properties ◽

Thermal Conductivity ◽

Compressive Strength ◽

Water Absorption ◽

Structural Properties ◽

Mechanical Milling ◽

Cement Mortar ◽

Cement Mortars

This work reports on the incorporation of Flint and Kaolin rocks powders in the cement mortar in an attempt to improve its mechanical properties and produce an eco-friendly mortar. Flint and Kaolin powders are prepared by dry mechanical milling. The two powders are added separately to the mortars substituting cement partially. The two powders are found to improve the mechanical properties of the mortars. Hardness and compressive strength are found to increase with the increase of powders constituents in the cement mortars. In addition, the two powders affect water absorption and thermal conductivity of the mortar specimens which are desirable for construction applications. Kaolin is found to have a greater effect on the mechanical properties, water absorption, and thermal conductivity of the mortars than Flint. This behavior is discussed and analyzed based on the compositional and structural properties of the rocks powders.

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