Ordinary Portland Cement Samples Research Articles

Natural carbonation of portland cement with synthetic zeolite Y as a supplementary cementitious material

Risks associated with carbonation are a key limitation to greater replacement levels of ordinary portland cement (OPC) by supplementary cementitious materials (SCMs). The addition of pozzolanic SCMs in OPC alters the hydrate assemblage by forming phases like calcium-(alumina)-silicate-hydrate (C-(A)-S-H). The objective of the present study was to elucidate how such changes in hydrate assemblage influence the chemical mechanisms of carbonation in a realistic OPC system. Here, we show that synthetic zeolite Y (faujasite) is a highly reactive pozzolan in OPC that reduces the calcium content of hydration products via prompt consumption of calcium hydroxide from the evolving phase assemblage prior to CO2 exposure. Suppression of portlandite at moderate to high zeolite Y content led to a more damaging mechanism of carbonation by disrupting the formation of a passivating carbonate layer. Without this layer, carbonation depth and CO2 uptake are increased. Binders containing 12–18% zeolite Y by volume consumed all the calcium hydroxide from OPC during hydration and reduced the Ca/(Si+Al) ratio of the amorphous products to near 0.67. In these cases, higher carbonation depths were observed after exposure to ambient air with decalcification of C-(A)-S-H as the main source of CO2 buffering. Binders with either 0% or 4% zeolite Y contained calcium hydroxide in the hydrated microstructure, had higher Ca/(Si+Al) ratios, and formed a calcite-rich passivation layer that halted deep carbonation. Although the carbonated layer in the samples with 12% and 18% zeolite Y contained 70% and 76% less calcite than the OPC respectively, their higher carbonation depths resulted in total CO2 uptakes that were 12x greater than the OPC sample. Passivation layer formation in samples with calcium hydroxide explains this finding and was further supported by thermodynamic modeling. High Si/Al zeolite additives to OPC should be balanced with the calcium content for optimal carbonation resistance.

Aloe Vera-Based Concrete Superplasticizer for Enhanced Consolidation with Limestone Calcined Clay Cement

Self-consolidating concrete (SCC) is renowned for its outstanding workability and ability to seamlessly flow into intricate structures with minimal vibrations, achieved through the incorporation of chemical admixtures. This study pioneers an innovative approach by exploring the use of the cost-effective and readily available plant extract aloe vera mucilage (AVM) as a bio-admixture for SCC. The primary objective is to assess the impact of AVM on SCC formulations, including those comprising ordinary Portland cement (OPC) and blended cement LC3 (clinker 50%, calcined waste clay 30%, limestone 15%, gypsum 5%). AVM is applied at varying dosages at up to 10%. Findings reveal that LC3 exhibits lower consistency, reduced slump values, and extended initial and final setting times compared to OPC. With increasing plasticizer dosage, V-funnel and L-box values decrease. Notably, OPC samples with both plasticizers outperform LC3 in compressive strength at 7, 14, and 28 days. Significantly, a 2.5% AVM dosage demonstrates enhanced compressive strength in both OPC and LC3 samples. In summary, this research positions AVM as an innovative and comparable alternative to commercial plasticizers, contributing to reduced yield stress and increased slump flow in SCC.

Application of cellulose nanocrystals in 3D printed alkali-activated cementitious composites

With the rapid development of concrete 3D printing for construction projects, it is crucial to produce sustainable 3D-printed cementitious composites that meet the required fresh and hardened properties. This study develops sustainable 3D-printed cementitious composites of ordinary portland cement and alkali-activated materials using cellulose nanocrystals (i.e., green natural nanomaterials). The extrudability and buildability of the alkali-activated slag-fly ash mixtures were improved and the extrusion pressure was reduced by ~ 35 % by increasing the cellulose nanocrystals content (up to 1 %) suggesting their viscosity-modifying properties in alkali-activated materials. The inclusion of cellulose nanocrystals improves the overall mechanical performance (8–20 % increase) and reduces the porosity of ordinary portland cement and heat-cured alkali-activated samples. Further, the addition of cellulose nanocrystals (up to 0.30 %) in sealed-cured alkali-activated samples improves their flexural strength by 20 %. The ordinary portland cement sample with cellulose nanocrystals densifies the microstructure and has an approximately 25 % increase in the degree of hydration at inner depths indicating cellulose nanocrystals' internal curing potential. The developed 3D-printable alkali-activated composites with cellulose nanocrystals can provide an overall reduction in the environmental impacts by eliminating/reducing the need for chemical admixtures to improve material consistency and stability, and replacing 100 % of portland cement.

Hybrid Nucleation Acceleration Method with Calcium Carbonate and Calcium Silicate Hydrate for Fast-Track Construction

This research focuses on achieving early strength of cement-based materials through the hybrid nucleation acceleration method. Through the study of various mortar mixtures, which incorporate components such as ordinary Portland cement (OPC), fine limestone powder (with a particle size of d50: 1 μm), coarse limestone powder (with a particle size of d50: 12 μm), calcium silicate hydrate (C-S-H) nucleation seeding agent, and calcium nitrate (CN), the effect of the hybrid nucleation acceleration method was investigated. When OPC was substituted with 20% fine limestone powder, a strength of 13.5 MPa was achieved at 6 h, whereas the use of coarse limestone powder only yielded 3.5 MPa within the same time frame. The mortar containing 2% C-S-H nucleation seeding agent reached an impressive 16 MPa at 6 h. Meanwhile, through the synergistic combination of fine limestone powder and C-S-H nucleation seeding agent, the 6 h early strength attained an impressive 19 MPa. The micrograph revealed that the hybrid nucleation acceleration method significantly promoted the formation of a dense network of C-S-H within the paste, thus enhancing the packing density. Measuring the heat release demonstrated that the samples accelerated with the C-S-H nucleation seeding agent and fine limestone reached the peak 160 min earlier than the OPC sample, indicating a faster hydration process. The hybrid nucleation accelerated concrete (HNAC) achieved strengths of 20 MPa and 27 MPa within 6 and 8 h, respectively, whereas the 28-day strength surpassed 70 MPa. The concrete equivalent mortar (CEM), derived from concrete, attained a compressive strength of 25 MPa within 8 h, making it suitable for repair applications. The modulus of rupture (MOR) was 7.31 MPa at 8 h and increased to 17.27 MPa at 28 days. Overall, the developed concrete and CEM with the novel hybrid nucleation acceleration method allowed for high early and long-term strength for fast-track construction to be attained.

Investigation on the influential mechanism of FA and GGBS on the properties of CO2-cured cement paste

In the present work, the synergetic effect of fly ash (FA) and ground granulated blast furnace slag (GGBS) on the early compressive strength and microstructure development of CO2-cured mortars was investigated. A rim of several micrometers was found around carbonated cement particles, which contained not only silica-rich gel but also crystal calcium carbonate. The calcium carbonate formed around the cement particles were surrounded by an amorphous layer of around 3 nm, while no layers were observed around the calcite formed on FA or GGBS particles. The calcite formed on FA particles were hexagonal plate shaped, while the one on GGBS particles were rhombohedral shaped. The use of FA resulted in the increase of crystal size and crystallinity of calcite, while GGBS decreased the crystal size of calcite. The incorporation of FA and GGBS increased the calcite content and polymerization of silica-rich gel. However, this didn't result in a higher compressive strength. This was due to the looser microstructure and nanopores within the carbonation products compared to the pure ordinary Portland cement sample. The compressive strength of the ternary binder system showed linear relationship with capillary pores and the crystal size of calcite. Moreover, the effect of GGBS on the compressive strength reduction was more obvious than that of FA.

Performance deterioration of municipal solid waste incineration fly ash-based geopolymer under sulfuric acid attack

This study assessed the durability of the geopolymer arranged from red mud-slag activated by carbide slag-municipal solid waste incineration fly ash (CRMG) as heavy metal solidification and stabilization binder exposed to sulfuric acid solution. Ordinary Portland cement (OPC) as control group. CRMG and OPC samples were immersed in solutions at pH = 3 and pH = 7 for 112 days. The sulfuric acid resistance of the samples was evaluated through visual observation, weight changes, compressive strength, as well as XRD, SEM, DTG, and FTIR. The results showed that CRMG had a higher acid buffering capacity than OPC in terms of visual appearance and mass loss. The compressive strength of CRMG slightly increased during the initial stage of immersion due to the production of geopolymer gel and the filling effect of a small amount of ettringite and gypsum, but decreased after 7 days due to the formation of a large amount of ettringite and gypsum which induce serious expansion and server cracking. CRMG's compressive strength remained higher than OPC's after 112 days of exposure to the acid solution, with a 20% loss in compressive strength. The leaching concentration of CRMG was far lower than the national standard. The study's conclusions could help reduce the environmental risks associated with solid waste disposal and provide a theoretical framework for the use of MSWI fly ash based geopolymer.

Investigations of the optimal requirements for curing of calcium sulfoaluminate cement systems

Wet curing improves ordinary portland cement (OPC) concrete durability and strength by increasing total hydration, densifying microstructure, and decreasing concrete permeability. In general, wet curing is recommended for OPC until it gains >70% of the designed compressive strength, typically for at least 7 days. Calcium sulfoaluminate (CSA) cement may allow for decreased curing time requirements due to its different phase composition from that of OPC, rapid hydration, and strength gain. Rapid hydration may also prevent some disadvantages associated with OPC curing requirements, such as long curing times, costs associated with the use of high-water quantities, and supervision needs for curing processes. In addition, it is important to understand the effect of use of various curing regimes that are currently specified for use with OPC when applied in CSA systems. This study investigated a variety of curing durations and curing solution compositions to understand their effects on CSA hydration, strength development, and shrinkage. The results demonstrate that 3-day moist curing promotes adequate strength gain and completion of hydration reactions. Additionally, wet curing CSA samples even for 1 day led to lower shrinkage than 7-day cured OPC samples and may result in reduced cracking in concrete pavements. Curing through ponding of samples in deionized water or calcium sulfate-saturated solution resulted in strength reductions of 18% or greater relative to fog-curing.

The Effect of Adding Concrete Wastes to Iraqi Ordinary Portland Cement

The research relied on taking five samples: The first sample is the Iraqi Ordinary Portland Cement. Physical tests were carried out for the purpose of comparison with other samples, as the rank of the Ordinary Portland Cement sample under study was 52.5R, according to the Iraqi specification No. 5, 2019. The second sample is concrete waste that was crushed then added water to it in known proportions according to the Iraqi specification and making a paste for concrete wastes only, but it failed to compressive strength and soundness. Three other samples of concrete waste 25%, 30%, and 35% with Ordinary Portland Cement as the addition of concrete wastes, were a partial substitute for the Ordinary Portland Cement. The results of the physical tests including fineness, setting time soundness, and compressive strength that were conducted on the third and fourth samples 25% and 30% were good results within the Iraqi specification No. 5, 2019. The result of physical tests at 35% of concrete wastes failed to test compressive strength. The results of mixing the concrete wastes with the Ordinary Portland Cement under consideration, showed that they can be mixed in various ratios and obtain different results. The more the concrete wastes mixed with the cement, the less the quality of the mixed cement was reaching the highest ratio that led to the failure of the mixture with the concrete wastes in terms of the physical properties. Basically, the mixture ratio of concrete wastes with the cement depends on the quality of the cement and its class in accordance with the compressive strength, and concrete waste quality.

Effect of Cu2+/SO42− ions concentration on the adsorption capacity of synthetic mayenite, its application for secondary adsorption process and utilization in cement samples

In this work, the effect of the concentration of Cu2+/SO42− ions on the primary adsorption capacity of synthetic mayenite, its thermal stability (after the first adsorption cycle), the application as a new effective secondary adsorption material, and, finally, the utilization in cement samples was examined.It was determined that mayenite samples can be applied for the removal of Cu2+/SO42− ions from the liquid medium; however, the adsorbed amount of Cu2+/SO42− ions and the efficiency of purification depend not only on the properties of the liquid medium, but also on the calcination temperature. It should be highlighted that, after the adsorption process, katoite, ettringite and partial carbonization compounds were formed. The thermal stability of the products after the adsorption processes was investigated within the 350–950 °C temperature range, and the products were later reused in the adsorption process. It was determined that the calcination (after the first adsorption process) of the products had positive influence on the adsorption capacity of Cu2+ ions and SO42− anions. After the second adsorption cycle, ettringite dominated across the entire range of products. The results of our hydration experiments showed that the above mentioned calcination product had a positive effect on the early hydration of Ordinary Portland cement samples. The obtained results were confirmed by X-ray, FT-IR, SEM/EDX, simultaneous thermal and heat release analyses.

Experimental Evaluation of Geopolymer Concrete Strength Using Sea Sand and Sea Water in Mixture

This paper presents the experimental strength evaluation of geopolymer concrete and ordinary concrete using sea sand and seawater in the mixture. A series of 30 cubic samples with a 150 mm side length and 12 rectangular specimens with a dimension of 100 × 100 × 400 mm (width × thickness × length) were cast and tested in this study. Specimens were divided equally into two groups. The first group of specimens was cast using geopolymer as the main binder (GPC), while the second group of samples was made using ordinary Portland Cement (OPC). While the compression tests were performed for specimens in two groups at the ages of 3, 7, 28, 60, and 120 days, the tensile tests were only performed for specimens at 7 and 28 days. The testing results revealed that the compression strength of GPC specimens using sea sand and seawater was significantly higher than that of OPC samples using the same type of salted sand and water. Besides, the use of sea sand and seawater for replacing river sand and fresh water in the production of GPC is feasible in terms of compressive strength since GPC produces a higher compressive strength than that of conventional concrete. Doi: 10.28991/CEJ-2022-08-08-03 Full Text: PDF

On the role of continuity in statistical nanoindentation of composite microstructures

AbstractThe validity of the statistical nanoindentation (SNI) technique for cementitious materials has been questioned by numerous researchers; however, it is still a commonly used method in literature. This study revisits assumptions pertaining to continuum mechanics of the method by using a well‐established selective SNI method to evaluate continuity in the mechanical response of each indent. Ordinary portland cement (OPC) was investigated alongside a two‐phase aluminosilicate ceramic (Al–Si). Filtering for continuity of indents eliminated a majority of indents in each sample. The indents meeting continuity requirements in the OPC sample had moduli values in the range of documented calcium silicate hydrates and portlandite—the predominant hydration phases in OPC. In the Al–Si sample, 73% of continuous indents were assigned to a mullite phase, although the chemical analysis showed only 42% mullite. This was attributed to the embedded morphology of the mullite phase, which made it more susceptible to structural compliance. These observations suggest that SNI may be ineffective for measuring the mechanical properties of individual phases in a microstructure if they are not prolific enough to exhibit a continuous indent response. Discontinuous indents due to microstructural interaction between phases were also shown to have a potential influence on the number of clusters (i.e., phases) suggested by the deconvolution algorithms.

The effect of calcined mayenite on the hydration of ordinary Portland cement

The synthesis of mayenite with differences in mineral composition and its influence on the properties of Ordinary Portland cement samples were examined. The synthesis of mayenite precursor was carried out in hydrothermal condition (CaO/Al2O3 = 2.8, w/s = 10) within 1–72 h at 130 °C. It was observed that synthetic precursor which was formed after 4 h remained stable only till 275 °C, and, at a higher temperature (350 °C), it fully decomposed to mayenite. In addition, when the temperature increases, the diffraction peaks typical to mayenite increases and changes mineral composition.It was found that the highest amount of mayenite additive (7.5 wt%) with differences in mineral composition has a positive influence on OPC hydration. It was observed that the mineral composition of additives has influence on the OPC hydration mechanism: at the first stage of hydration, the calcination temperature exerts negative influence on the formation of ettringite; at the second hydration stage, the reaction of gypsum with the additive calcined at 900 °C is more accelerated. The mechanism of hydration (21–60 min) depends mostly on the calcination temperature of the additive. At this stage, ettringite in the systems OPC -mayenite (synthesized at 350 °C) and OPC - mayenite (synthesized at 900 °C) is partially decomposed into monosulfoaluminate and gypsum. Meanwhile, the new exothermic reaction between mayenite and ettringite in the OPC- mayenite (synthesized at 550 °C) system promoted the formation of monosulfoaluminate and hydrated calcium aluminate compounds.

Enhanced carbonation curing of cement pastes with dolomite additive

AbstractCarbonation curing of cement‐based materials has recently received increasing attention as a CO2 utilization technology. This study aimed at investigating the effects of carbonation curing on the performance of ordinary Portland cement (OPC) pastes with dolomite additive (DPC). The CO2 uptake capacity, after being normalized to carbonation active components, significantly increased with larger dolomite mixing ratios. For DPC‐25% samples under 2.5 MPa curing pressure, the maximum CO2 uptake capacity reached 23.6 wt%, which was 23% higher than that of pure OPC samples under the same condition. Effects of water to solids (w/s) ratio and temperature on carbonation are two‐sided. The optimum w/s ratio for CO2 uptake capacity of DPC‐15% samples was approximately 0.20, while the optimum temperature was equal to 60℃ or higher than 60℃. The CO2 uptake capacity increased with finer particle size and higher CO2 curing pressures. Compared to large particles, smaller particles are more likely to have a better dilution effect, providing more contact surface for carbonated precipitation. From the pore structure changes perspective, carbonation products filled the interface between the dolomite and amorphous particles. DPC‐25% samples with higher dolomite mixing ratios provided more pores and pathways for gas diffusion, and exhibited a more uniform structure, thereby contributing to the highest compressive strength values of DPC‐25% samples (63.8 MPa) among all the DPC samples. These findings imply the possible feasibility of dolomite as an additive in carbonation cured building materials. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

Mechanistic insights into the dynamics of radionuclides retention in evolved POFA-OPC and OPC barriers in radioactive waste disposal

Cementitious barriers are widely used in all radioactive waste disposal facilities to ensure the fulfillment of several safety functions. A realistic quantification of radionuclide retention characteristics into these barriers under the dynamic changes that occur in the disposal facility is necessary to optimize the design of the facility and ensure the reliability of these safety functions. Herein, the beneficial use of Palm Oil Fuel Ash (POFA) as supplementary material to tailor the radionuclide retention characteristics of Ordinary Portland Cement (OPC) is investigated. The characterizations of evolved OPC and POFA-OPC samples revealed that the use of POFA slows down the carbonation process; enhances the formation and polymerization of low Ca/Si C-S-H and reduces the degradation state of the barrier. The effects of the progressive release and cooling down of Cs sources and progressive water intrusion on the retardation coefficients, relative contaminant retention, and capacity factors were investigated assuming the validity of the local linear and Langmuir based models. In comparison with reference OPC samples, it was found that POFA improved greatly the containment performance, where the retardation coefficients in the supplemented material are in the range (33–35.42) under the coupled effects of progressive release and cooling down of Cs sources. The retardation coefficients and the barrier capacities increased largely in very diluted systems. The adaptation of the local linear isotherm to describe the dynamic changes in the disposal facility was found to be associated with considerable uncertainties that need to be thoroughly identified.

Compatibility between Rice Straw Fibers with Different Pretreatments and Ordinary Portland Cement.

The compatibility between crop straw and Portland cement greatly restrict the application of crop straw in cement-based materials. In this study, rice straw fibers with different pretreatments were added to ordinary Portland cement (OPC), and the influence of different rice straw fiber (RF) content on the hydration process of OPC was measured using calorimeter tests. Additionally, compatibility between RF and OPC was evaluated using the inhibitory index. As a result, steam explosion treatment of rice straw removed most hemicellulose and post-treatment bleaching was used for delignification. As compared with the pure OPC, addition of RF inhibited the hydration of OPC, and the inhibition degree reduced with the increase in pretreatment degree of RF. The inhibitory index grade of different RF filled OPC (RF-OPC) samples is directly related to hemicellulose and lignin content. Compared with lignin, hemicellulose has a greater influence on cement hydration. Without considering the influence of other components, the RF-OPC samples with hemicellulose content of 1.54 wt.% reached the inhibitory index extreme grade, and the hemicellulose content of 2.05 wt.% led to the cessation of cement hydration. The inhibitory index of the samples with 2.05 and 0.85 wt.% lignin content is moderate and low grade, respectively. In addition, the results of XRD patterns and SEM images are consistent with those of heat of hydration. In terms of mechanical properties of cement-based composites with 10 wt.% rice straw fibers, pretreatment of fibers is beneficial to improving the fracture toughness of the samples.

Chloride ion binding effect and corrosion resistance of geopolymer materials prepared with seawater and coral sand

In this work, the chloride binding capacities and chloride diffusion resistance of alkali-activated fly ash and slag powder geopolymer systems prepared with seawater and coral sand are investigated. Through the macro tests (e.g., chloride ion binding ratio, electric flux, etc.), stripping C-S-H, C/N-A-S-H from anhydrous particles and a variety of microscopic tests (e.g., MIP, XRD, SEM-EDS), the chloride binding mechanism of ordinary Portland cement (OPC) and geopolymer are analyzed and compared. The result shows that the chloride binding capacity of geopolymer samples under standard curing is better than that of OPC samples under the same condition (for instance, the 28-day chloride binding coefficient of geopolymer (FS1): 83.372%, OPC (R1): 73.223%). And the binding of chloride ion can be improved to a certain extent by increasing the initial chloride concentration. Geopolymer bounds the chloride ions through physical absorption or chemical reaction with cement compositions. The porous structure of C/N-(A)-S-H gel and high content of Al element promote the chloride binding capacity. The additional porous coral sand can reduce the chloride resistance capacity of specimens. But with slag proportion increasing, the geopolymer shows better chloride resistance capacity (for example the chloride diffusion coefficient decreases by 98% from 152.61 m2/s to 2.86 m2/s when slag proportion increased from 10% to 90%). The chloride diffusivity of geopolymers measured by the electric flux method has a large deviation, which is not suitable for direct evaluating of resistance to chloride penetration of geopolymer system.

Significance of properly proportioned fly ash based blended cement for sustainable concrete structures of tannery industry

Tannery wastewater contains several detrimental constituents that severely affect concrete durability. It can also cause soil and water pollution from discharge of untreated effluent if not properly contained. Therefore, ensuring proper protection of tannery wastewater treatment plants is of extreme importance to prevent leaching of hazardous wastewater. Properly proportioned blended cement is usually required for construction of tannery wastewater treatment plants to ensure structural stability. However, there is no definite guideline available for mix design of concrete structures exposed to tannery wastewater. In this study, effect of adding different proportions of two industrial wastes i.e. fly ash and granulated blast furnace slag with ordinary Portland cement (OPC) as supplementary cementitious material (SCM) has been investigated under tannery wastewater conditions. A total of 240 cubes and 48 mortar bars were prepared and tested under normal and simulated tannery wastewater conditions. The performance was measured in terms of compressive strength, expansion, weight loss, surface deterioration etc. Scanning Electron Microscope (SEM) images and Energy-dispersive X-ray Spectroscopy (EDS) techniques were used to observe changes in microstructure. Test results revealed that blended cement composites with fly ash and/or slag suffered less strength and weight loss under tannery wastewater as compared to OPC samples. However, only fly ash blended cement composites exhibited desired performance under expansion test. In addition, SEM images and EDS analyses confirmed lower density of ettringite and less leaching of calcium in fly ash blended mixes due to pore refinement caused by formation of secondary hydration products.

Compressive strength and microstructure of modified coffee exocarp cement-based composites

Portland cement-based composites were prepared with coffee exocarp (pretreated with water or NaOH) via vacuum extraction technology. An orthogonal test was adopted to analyze the influence of various factors on mechanical properties of the composite. The morphology and composition of the pretreated coffee exocarp and composites were analyzed via environmental scanning electron microscopy and X-ray diffraction, respectively. The results showed that the coffee exocarp content and vacuum extraction time significantly affected the compressive strength. An addition of 10% coffee exocarp had a slight negative effect on the mechanical properties but enhanced the crack inhibition and overall toughness of the composite. The scanning electron microscopy and X-ray diffraction results showed that the composite containing coffee exocarp pretreated with 4% NaOH solution had the highest density and exhibited the best properties due to mechanical interlocking between the coffee exocarp and cement. After 28 d of curing, the composites exhibited a maximum compressive strength of 15.72 MPa, a mass that was approximately 37% less than that of ordinary Portland cement samples, and a bulk density of 1.5 g/cm3 to 1.6 g/cm3. Hence, the produced biocomposites could be used for low-load pavements, providing a new type of economical building material.

Comparison of mechanical behaviour of geopolymer and OPC-based well cement cured in saline water

Well cement plays a vital role in maintaining wellbore integrity in a carbon capture and storage project. To date, ordinary Portland cement (OPC)-based well cement has been used and there are contrasting research findings on its suitability as well cement. This research aims to use geopolymer as well cement, and major aim of this work is to analyse the mechanical behaviour of both geopolymer and OPC subjected to various down-hole conditions including different salinity (0–30% NaCl) and confinements (0–15 MPa). This research comprises experimental and numerical works. Under the experimental work, series of unconfined compressive strength (UCS) test were conducted for geopolymer and OPC samples cured in saline water with 0–30% NaCl salinity for a period of 45 days. COMSOL multiphysics software was used for the numerical study, and first, laboratory scale uniaxial stress–strain behaviour of both geopolymer and OPC was validated numerically. The model was then extended to study the triaxial mechanical behaviour under different salinity (0–30% NaCl) and confining pressures (0–15 MPa) conditions. Based on the results, it was noticed that UCS of geopolymer increases with salinity due to the high resistance against alkali leaching in saline water compared to fresh water. The UCS of OPC increases with salinity up to 10% NaCl, and then it reduces with any further increase in salinity. The UCS of geopolymer is 6% to 66% higher than that of OPC depending on the salinity conditions and geopolymer possesses higher UCS than OPC for any given salinity condition. COMSOL multiphysics numerical software predicted the stress–strain behaviour of geopolymer and OPC accurately up to yield point. Failure strength of geopolymer in saline water is 3% to 61% higher than that of OPC for a given confining pressure. Findings of this research indicate that geopolymer can be a good alternative for OPC based well cement under deep down-hole conditions.

Sugarcane bagasse and rice husk ash pozzolans: Cement strength and corrosion effects when using saltwater

The production of ordinary Portland cement (OPC) contributes to the release of harmful greenhouse gases. In an effort to reduce these emissions, this study explores biomass materials to evaluate their use as partial replacements for ordinary Portland cement. Rice husk and sugarcane bagasse are agricultural waste products and large amounts of these are currently landfilled, making them inexpensive and available. When combusted at high temperatures they form rice husk ash and sugarcane bagasse ash with pozzolanic characteristics. The high silicon dioxide levels in these products make them good options to use as partial replacement for OPC. Replacement with 20% rice husk ash or 10% sugarcane bagasse ash give similar compressive strength and corrosion resistance for hardened cement paste samples compared to control OPC samples, if appropriate amounts of plasticizer are used. Porosity as measured by water adsorption trended higher with increased water to cement ratio due to replacement of cement with pozzolan, since water to binder ratio remained constant at 0.45:1. This study used saltwater in the mix, to investigate the use of a resource that requires less energy use in ocean-bordering areas.