Metakaolin Concrete Research Articles

Statistical Model for Compressive Strength of Metakaolin Concrete

In the present research work, investigations were carried out to improve the performance of concrete in terms of strength by incorporating metakaolin (MK) as mineral admixture in concrete. Parametric study was carried out by considering w/c ratio, various percentage of MK and age of concrete as parameters to understand the effect of each parameter. The study was conducted for different w/c ratios of 0.32, 0.35, 0.4 and 0.5. The MK proportion was varied from 0 to 15% with an increment of 5% and age of concrete from 3 to 90 days were considered and experiments performed accordingly. The effects of above said parameters on the various properties of concrete such as workability, compressive strength and pH of concrete were investigated, and the results of metakaolin concrete were compared with the conventional concrete. From the results, it was observed that MK concrete showed greater strength for higher water cement ratios (0.4 & 0.5). A Multiple non-linear regression analysis was used to develop a statistical model to predict the strength and found to have good correlation between the observed and predicted values. It was concluded that the concrete developed in this study have significant potential for use on real time projects.

EXPERIMENTAL INVESTIGATION OF THE DURABILITY PROPERTIES OF CONCRETE PRODUCED WITH METAKAOLIN AS PARTIAL REPLACEMENT OF CEMENT

The research investigates the durability properties of concrete produced with metakaolin (MTK) as partial replacement of cement. Cement was partially replaced by metakaolin at 5% to 30% at an interval of 5%. Physical properties of materials were tested. A 100 x 100 x 100mm cube was used for density, compressive strength, water absorption and abrasion resistant test, while, 100mm x 200mm cylinder was used for split tensile strength, at a mix ratio of 1:2:4 with 0.5 w/c ratio, and cured at 7, 14, 28, 56 and 90 days under different curing conditions. Result shows that the density of concrete increase as the curing ages of concrete increases. The highest compressive strength of concrete at 28days was at 0% control which achieved 28.2 N/mm2 and 27.6 N/mm2, while, 10% has the highest strength of 32.1 N/mm2 and 31.1 N/mm2 at 90 days for concrete cured in H2SO4 and MgSO4 respectively. 10% MTK concrete has reduce absorption capacity of 11.34, 11.17% and 6.57% in H2O, H2SO4 and MgSO4 respectively, as compared to that of control concrete, and has improve resistance to abrasion in aggressive environment. Chemicals significantly affect the strength of concrete. MgSO4 is more deleterious to concrete than H2SO4. In conclusion, metakaolin is a suitable pozzolana for use in the production of concrete, at lower volume of replacement will enhance the reduction of cement usage in concretes, thereby reducing the production cost and environmental pollution from exploration and production of cement. 10% MTK is the optimum percentage in concrete, therefore,...

Effect of Water Magnetization Technique on the Properties of Metakaolin-Based Sustainable Concrete

Using metakaolin (MK) in concrete with magnetized water (MW) has a high possibility to enhance concrete suitability. In this study, the effect of using MK and MW on concrete characteristics was studied through testing twelve concrete mixes. Seven ratios of MK were used in this study, namely 0%, 5%, 10%, and 20%, as an alternative to cement and +5%, +10%, and +20% as a cement additive. In addition, five water magnetization methods were applied on MK concrete. In the first stage of this study, the impact of different MK ratios on the workability of concrete, compressive strength, flexural strength, and tensile strength was studied using traditional tap water (TW) as the concrete mixing water. In the second stage, the best mix (best MK ratio) from the first stage was chosen to study the effect of the water magnetization method on concrete properties and to determine the best method for water magnetization. Scanning electronic microscope (SEM) analysis was also carried out on selected mixes to closely investigate the effect of MK and MW on concrete microstructure. The results showed that the best ratio of MK in concrete was +10% (MK as a 10% cement addition), and the best water magnetization method was to pass the water through 1.6 tesla then through 1.4 tesla magnetic fields. The SEM analysis confirmed the absence of pores after using MW instead of regular TW by increasing the calcium silicate hydrate (CSH) gel and reducing calcium hydroxide (CH). Using MK and MW enhanced the compressive strength by up to 33%, 32%, and 27% at 7, 28, and 365 days, respectively, and MW enhanced the workability by up to 3% compared to that of the control mix.

Investigating the environmental and economic impacts of using supplementary cementitious materials (SCMs) using the life cycle approach

Concrete production significantly contributes to the construction industry's carbon emissions and resource depletion. Replacing Portland cement with supplementary cementitious materials (SCMs) can improve the sustainability and performance of concrete. However, limited holistic research compares SCMs considering environmental, economic, durability, and strength criteria. This study comprehensively evaluates supplementary cementitious materials (SCMs) in concrete production using life cycle assessment. The SCMs examined were rice husk ash (RHA), sugarcane bagasse ash (SCBA), metakaolin (MK), and trass. The study quantified CO2 emissions, cost, compressive strength, and service life of concrete mixes with these SCMs and compared them to ordinary Portland cement concrete. The findings reveal that the 15 % metakaolin replacement sample had the best overall performance. It reduced CO2 emissions of one m3 of concrete per year of service life by 83 % and costs of one m3 per year by 78 % compared to ordinary concrete. The metakaolin concrete also increased the compressive strength by 25 % and extended the service life from 8 to 43 years in a marine environment. Among the SCMs, RHA demonstrated a 90 % reduction in CO2 emissions per service life year and unit compressive strength compared to ordinary concrete. SCBA had the highest cost due to high production requirements. Trass offered a 44 % decrease in CO2 emissions per service life year and unit compressive strength. The results highlight metakaolin's optimal balance between sustainability and performance. The reduced CO2 emissions demonstrate SCMs' potential to lower the construction industry's carbon footprint. The study offers original data and insights to enable greener and lower carbon concrete production using supplementary cementitious materials.

Accelerated curing effects on performance of metakaolin concrete

AbstractThe manufacturing of cement liberates the green-house gasses into atmosphere. To overcome this problem so many alternative materials has been invented by researchers to minimize addition of cement. The incorporation of these alternative materials as cementitious material in concrete enhances the attributes of concrete. In this scenario metakaolin gained momentum as a substitution to cement in concrete. Most of the researchers studied the performance of concrete incorporating metakaolin as cementitious material in normal curing conditions. There is a need for analysing the impact of accelerated curing on properties of concrete by incorporating metakaolin as cementitious material. The current construction industry needs high early strength for removal of form work in early ages. The accelerated curing is a method which provides high early strength. In this study, different proportions of metakaolin are added as partial alternative to cement and cured in accelerated curing tank for 3.5 h. The strength parameters test, durability test, and micro-structural parameter tests are performed on these samples. Further, micro-structural analysis has been carried out using SEM, and EDX tests. Results depicted the incorporation of 15% of metakaolin as substitute to cement amplifies the overall performance of concrete in accelerated curing regime.

CO2 emission analysis of metakaolin and alccofine replaced cement in M40 grade concrete.

Among the largest CO2 emission industries, the cement industry is ranked in 2nd place. A large volume of CO2 is emitted at the clinker production, which is a cement manufacturing intermediate product. Countries around the world were having difficulty reducing atmospheric emissions of greenhouse gases (GHG). Concrete is still being used more and more as the nation's infrastructure advances. The amount of CO2 emitted by concrete can be decreased by using less cement or substituting other materials for cement. In this study, the CO2 emission analysis is made on M40 grade, which is that metakaolin (MK) and alccofine (AL) are replaced to the cement in the manufacturing of concrete and is compared with the conventional concrete. The optimum cement replacement of MK and AL is 10% in the production of M40 grade concrete. MK and AL concrete have advantages and disadvantages. If proper safety precautions are taken during the manufacturing process, the toxicity level can be reduced, as well as the amount of CO2 released by the cement during the production of concrete. The LCA (life cycle analysis) is made for the concrete specimens, and the results were interpreted to know which concrete sample emits less and more carbon dioxide. The LCA study provided insights into the environmental aspects of metakaolin and alccofine concrete, including potential reductions in CO2 emissions, energy consumption and other environmental indicators. It helps identify areas of improvement and informs decision-making processes regarding sustainable material choices and construction practices. In M40 grade concrete, a 10% cement replacement with metakaolin and alccofine was found to be ideal. These results could also help in identifying the major cause of CO2 emission, and they can be used for further research purposes.

Long term durability assessment of self-compacting concrete made with crushed recycled glass and metakaolin

Sustainable production in construction industry can only be possible through a proper management and conservation of limited natural resources such as fine aggregates. This challenge can be tackled by efficient utilization of discarded waste material such as glass in production of sustainable concrete. This paper investigates the use of crushed recycled glass (CRG) and metakaolin (MK) in development of durable self-compacting concrete (SCC). Four groups of SCC mixtures were prepared using different proportions of CRG (0–50%), while keeping MK concentration equal to 0%, 4%, 8% and 12%. Durability performance of SCC was accessed using water absorption, sorptivity, chloride ion permeability, drying shrinkage, water penetrability under pressure and alkali-silica reaction (ASR) tests. As the CRG content increased, group 4 (having 12 % MK) was most efficient in improving drying shrinkage and pressurized water penetration results; whereas Group 1 (0% MK mixtures) exhibited a minimal change. Raising CRG content in the mix resulted in decrease of water absorption and chloride ion penetration for all groups with group 4 exhibiting maximum reduction. ASR testing revealed that incorporating glass at a higher concentration (40% and 50%) resulted in excessive expansion (more than prescribed limit of 0.1%), which can be suppressed by partially substituting cement with MK. FE-SEM and TGA analysis were carried out to understand the mechanism behind these changes, which revealed that the secondary hydration products formed by addition of MK in concrete can densify the pore structure and refine CRG particle-cement paste interfacial micro-crack width (was evident from FE-SEM micrographs), thus improving the durability of concrete. Indeed, simultaneous incorporation of CRG and MK proved to be advantageous for development of green SCC.

Effect of Cooling Conditions, Retrofitting on Strength of Concrete Subjected to Elevated Temperature

Concrete has a high degree of fire resistance at moderate temperatures. High temperatures, however, cause concrete to lose its stiffness and strength. The effects of cooling techniques and retrofitting on the strength of concrete exposed to high temperatures have not been synchronized in previous studies. This experimental research aims to evaluate the effect of cooling conditions and the effectiveness of retrofitting concrete subjected to elevated temperatures. Four types of concrete: M 20 normal concrete (NC); M 20 metakaolin concrete (MC); M 40 standard concrete (SC); and M 40 self-compacting concrete (SCC) are considered in this study. A total of 864 samples consisting of cube, beam, and cylinder specimens are subjected to sustained elevated temperatures of 400oC, 600oC, and 800oC for 2 hours rating. The weight and strength of half of the heat-damaged samples are assessed following natural air cooling (NAC) and water jet cooling (WJC). The remaining 50% of samples retrofitted with carbon fiber reinforced polymer (CFRP) are tested to evaluate the upgraded strength. The experimental findings demonstrate that water jet cooling (WJC) causes more strength degradation, and CFRP proves to be effective in restoring the strength of heat-deteriorated specimens. Overall, self-compacting concrete (SCC) has shown high resistance to elevated temperatures. Doi: 10.28991/CEJ-2023-09-07-013 Full Text: PDF

Modelling the compressive strength of high-performance concrete containing metakaolin using distinctive statistical techniques

Cement consumption is rapidly increasing around the world causing environmental concerns over higher CO2 emissions. Metakaolin obtained through the calcination of kaolinite clay is an eco-friendly substitution for clinker in portland cement production. The raw materials required to produce metakaolin are easily accessible and cheap. Addition of metakaolin in concrete alters mechanical properties, notably compressive strength. Prior knowledge of the strength characteristics of concrete play a vital role in determining the design aspects of the buildings. Robust prediction models that can effectively predict the compressive strength of pozzolan-based concrete are highly essential in the field of concrete technology in order to save time and reduce laboratory testing samples. In this regard, A total of 152 experimental datasets from the literature were collected and evaluated. Influencing parameters such as binder content (385–600 kg/m3), water to cementitious material ratio (0.25–0.45), metakaolin replacement levels (0%–50%) and SiO 2/Al2O3 ratio in the cement paste (1.05–12) were chosen as independent variables. The present study was aimed at developing prediction models using different statistical techniques such as Linear regression (LR), Multi-logistic regression (MLR), Nonlinear regression (NLR) and Response surface methodology (RSM) to predict the 28-day compressive strength of High-performance concrete containing metakaolin. Also, the performance of the proposed models was examined using different statistical metrics such as coefficient of correlation (R), root mean squared error (RMSE), mean absolute error (MAE) and scatter index (SI). The quadratic RSM model outperforms all the proposed models in the present study with R, RMSE, MAE and SI of 0.92, 6.5 MPa, 5.2 MPa and 0.08. The models were evaluated in strength ranges other than HPC, and the QRSM model showed a maximum residual error of ±20%. Furthermore, the results of sensitivity analysis indicate that binder content, w/b ratio and SiO2/Al2O3 are the most influential parameters controlling the compressive strength of concrete.

Characteristics of Sustainable Concrete Containing Metakaolin and Magnetized Water

In this study, fourteen sustainable concrete mixes containing metakaolin (MK) as supplementary cement material (SCM) and magnetized water (MW) as concrete mixing water were designed, prepared, tested, analyzed, and compared. The MK was used as a partial replacement of cement weight by 5%, 10%, and 20%, and as an additive to cement by 5%, 10%, and 20% of cement weight. The MW was used to fully replace tap water (TW) in concrete mixes and was prepared using two different magnetic fields of 1.4 tesla (T) and 1.6 T. This experimental research aimed to assess the characteristics of concrete manufactured with MK and MW. The mechanical and durability characteristics of fresh and hardened concrete were measured for the assessment. Microstructural and chemical analyses were carried out on selected materials and concrete mixes. The workability and compressive strength of the materials at 7, 28, and 365 days were measured, in addition to the splitting tensile strength at 28 days and the flexural strength at 28 days. The compressive strength at 365 days was conducted at 18 °C and 100 °C to study the effect of the applied variables on the concrete durability at different elevated temperatures. The microstructural and chemical analyses were conducted using a scanning electron microscope (SEM), energy dispersive X-ray (EDX), and Fourier transform infrared (FTIR) spectroscopy. The results showed that using 10% MK as a cement additive was the best ratio in this study, which enhanced all the measured mechanical characteristics when the TW or MW was used. Using MW instead of TW in MK concrete increased all the mechanical properties measured at 28 days by about 32–35%. The results of the microstructural and chemical analyses supported the compressive strength increase by showing indications of more C-S-H gel production and less CH when using MW in MK concrete. In addition, fewer micro-cracks and pores, and relatively denser concrete, were detected when using MW with 10% MK as a cement additive.

A comprehensive GEP and MEP analysis of a cement-based concrete containing metakaolin

Due to the detrimental environmental consequence of cement formation, studies has concentrated on decreasing the environmental influence and expense of cement containing products. It is crucial to conduct research on the mechanical characteristics of cement additive/replacement products such as metakaolin (MK). To serve the said purpose, the importance of developing predictive machine learning (ML) models is growing as ecological concerns intensify. Since there are few ML approaches for them, it is imperative to develop techniques to improve the mechanical properties of such products. In order to overcome these issues, this research examines ML methods for forecasting the compressive strength (fc') of concrete containing MK. Gene expression programming (GEP) and multigene expression programming (MEP), two distinct ML predictive models, are provided in detail along with the most useful variables, enabling effective analysis and forecasting of the fc' of concrete containing MK. An important component of any prediction or simulation endeavor is model generalization, and the researchers of this study used a data set of MK concrete mechanical properties for this purpose. The database has 405 data points with pertinent model parameters to calculate the fc' of concrete containing MK. Cement, percentage of metakaolin by binder, coarse and fine aggregate by binder, water by binder, coarse aggregates by fine aggregates, percentage of superplasticizer by binder, and age are among the factors in the database that influence concrete's fc' yet still previously infrequently regarded as crucial input attributes. The effectiveness of the models is then examined in order to choose and implement the best predicted model for the mechanical properties of MK-based concrete. According to the findings of this research, the optimal ML algorithms for forecasting MK-based concrete fc' is MEP with R2 value of 0.96. Additionally, the sensitivity analysis shows that water-by-binder, percentage of superplasticizer-by-binder and age have the significant effect on the development of compressive strength of metakaolin based concrete. GEP and MEP models develop empirical expression for the outcome to forecast future databases' features to promote the usage of sustainable MK concrete. Moreover, detrimental effects caused by intensive and costly labor work can be overcome by utilizing these environmental-friendly techniques.

Influence of pore structure on corrosion resistance of high performance concrete containing metakaolin

Even though concrete is considered to be durable, the environment to which the concrete is exposed plays an important role in its durability. The durability of concrete is challenged due to its porous nature, which is especially important in harsh exposure conditions such as marine environment. The reinforced concrete elements of marine structures such as bridges, wharves, docks, etc. are subjected to various types of exposures such as wetting and drying action [WDA], fully submerged condition, and in contact with chlorides. To refine the pore structure of concrete and to improve the durability characteristics of such structures, it is essential to use high performance concrete [HPC]. In this study, metakaolin [MK] is used as partial replacement of cement to produce HPC. The use of metakaolin is found to be very effective in reducing the porosity of concrete. As the porosity of concrete decreases, the corrosion rate can be reduced considerably. The durability characteristics of metakaolin-incorporated HPC is studied for 365 days to investigate the changes in its pore structure in long term. The iCOR® NDT method is used to find the corrosion performance and concrete resistivity of high performance metakaolin concrete under a simulated wetting and drying action [WDA] of seawater over several periods. The deterioration effect caused by the simulated WDA of seawater is also studied by considering the bond strength of specimens subjected to normal and corrosive exposure conditions.

Chemical Evolution of Pore Solution in Metakaolin Concrete During Water Evaporation

Metakaolin concrete is a kind of porous material, which contains a variety of chemical ions in the pores. Solutions in these pores are exposed to the atmosphere and exist evaporation and condensation processes, therefore, the pore solution volume of concrete changes all the time. When the ion concentration in the pore solution changes, it has an important impact on the strength development and durability of concrete. However, the real-time monitoring of the concentration of pore solution was difficult. To study the chemical evolution of pore solution in concrete, the variation of saturated vapor pressure on the surface of metakaolin concrete was studied based on the Cisternas-Lam rule. The evaporation rate of solvent in the pore solution of concrete under the corresponding saturated vapor pressure in this paper was studied by the Stefan diffusion method. The dynamic equilibrium process equation of ions in pore solution was then established based on the thermodynamic equilibrium equation. Based on the above model, the change process of the pore solution of metakaolin concrete was studied, and it was verified by the results of the literature.

Use of E-Waste in Metakaolin Blended Cement Concrete for Sustainable Construction

This paper investigates the use of non-metallic portion (NMP) reclaimed from e-waste (i.e., waste printed circuit board—PCB) as replacement of natural sand in the blended cement concrete by using Metakaolin (MK) as supplementary cementitious material for its effect on the mechanical, durability, microstructural, and mineralogical properties of concrete. It was found that the blended mixes containing NMP and MK outperformed the control mix. With the addition of 10% NMP and 10% MK, the maximum compressive strength was obtained, with the splitting tensile and flexural strength following the same trend. The performance of the mixes was lowered above 10% replacement levels, although it was still better than the control mixture. When compared to other mixes, 10% NMP and 10% MK concrete had the lowest sorptivity and water absorption values, as well as the highest resistance to chloride-ion penetration. FESEM was used to confirm the results, and then XRD was used to determine the elemental classification. This study lays the groundwork for a long-term strategy for utilising NMP and MK as extremely effective concrete additives.

Mechanical and Durability Evaluation of Metakaolin as Cement Replacement Material in Concrete.

Due to the increasing prices of cement and its harmful effect on the environment, the use of cement has become highly unsustainable in concrete. There is a considerable need for promoting the use of cement replacement materials. This study investigates the effect of variable percentages of metakaolin (MK) on the mechanical and durability performance of concrete. Kaolin clay (KC) was used in the current research to prepare the MK by the calcination process; it was ground in a ball mill to its maximum achievable fineness value of 2550 m2/Kg. Four replacement levels of MK, i.e., 5%, 10%, 15%, and 20% by weight of cement, in addition to control samples, at a constant water-to-cement (w/c) ratio of 0.55 were used. For evaluating the mechanical and durability performance, 27 cubes (6 in. × 6 in. × 6 in.) and 6 cylinders (3.875 in. diameter, 2 in. height) were cast for each mix. These samples were tested for compressive strength under standard conditions and in an acidic environment, in addition to being subjected to water permeability, sorptivity, and water absorption tests. Chemical analysis revealed that MK could be used as pozzolana as per the American Society for Testing and Materials (ASTM C 618:2003). The results demonstrated an increased compressive strength of concrete owing to an increased percentage of MK in the mix with aging. In particular, the concrete having 20% MK after curing under standard conditions exhibited 33.43% higher compressive strength at 90 days as compared to similarly aged control concrete. However, with increasing MK, the workability of concrete decreased drastically. After being subjected to an acid attack (immersing concrete cubes in 2% sulfuric acid solution), the samples exhibited a significant decrease in compressive strength at 90 days in comparison to those without acid attack at the same age. The density of acid attack increased with increasing MK with a maximum corresponding to 5% MK concrete. The current findings suggest that the local MK has the potential to produce good-quality concrete in a normal environment.

In-Depth Analysis of Cement-Based Material Incorporating Metakaolin Using Individual and Ensemble Machine Learning Approaches.

In recent decades, a variety of organizational sectors have demanded and researched green structural materials. Concrete is the most extensively used manmade material. Given the adverse environmental effect of cement manufacturing, research has focused on minimizing environmental impact and cement-based product costs. Metakaolin (MK) as an additive or partial cement replacement is a key subject of concrete research. Developing predictive machine learning (ML) models is crucial as environmental challenges rise. Since cement-based materials have few ML approaches, it is important to develop strategies to enhance their mechanical properties. This article analyses ML techniques for forecasting MK concrete compressive strength (fc'). Three different individual and ensemble ML predictive models are presented in detail, namely decision tree (DT), multilayer perceptron neural network (MLPNN), and random forest (RF), along with the most effective factors, allowing for efficient investigation and prediction of the fc' of MK concrete. The authors used a database of MK concrete mechanical features for model generalization, a key aspect of any prediction or simulation effort. The database includes 551 data points with relevant model parameters for computing MK concrete's fc'. The database contains cement, metakaolin, coarse and fine aggregate, water, silica fume, superplasticizer, and age, which affect concrete's fc' but were seldom considered critical input characteristics in the past. Finally, the performance of the models is assessed to pick and deploy the best predicted model for MK concrete mechanical characteristics. K-fold cross validation was employed to avoid overfitting issues of the models. Additionally, ML approaches were utilized to combine SHapley Additive exPlanations (SHAP) data to better understand the MK mix design non-linear behaviour and how each input parameter's weighting influences the total contribution. Results depict that DT AdaBoost and modified bagging are the best ML algorithms for predicting MK concrete fc' with R2 = 0.92. Moreover, according to SHAP analysis, age impacts MK concrete fc' the most, followed by coarse aggregate and superplasticizer. Silica fume affects MK concrete's fc' least. ML algorithms estimate MK concrete's mechanical characteristics to promote sustainability.

Influence of Colloidal Silica and Partial Replacement of Cement with Metakaolin in Concrete

High strength concrete is being required due to the construction industry's growth. Admixture and supplemental cementing materials (SCMs) are employed to attain this strength. According to earlier research, nanoparticles with a high surface area to volume ratio, such as colloidal nano-silica (CS), which contains an amorphous silicon dioxide (SiO2) core and a hydroxylated surface, have the potential for extremely high chemical reactivity. This study examined the results of adding metakaolin and colloidal silica to concrete in varying amounts. Tests in accordance with Indian standards have been conducted in order to evaluate and compare the mechanical properties of concrete, such as compressive strength, split tensile strength, and flexural strength, while employing different percentage replacements of metakaolin and colloidal silica. According to Indian norms, 150mm cubes were cast for compressive strength tests and 150mm diameter by 300mm height cylinders were produced for split tensile strength tests. In the investigation, metakaolin was used in instead of 10 to 30 percent cement mass, and 0 to 6 percent colloidal silica was added. The results of the experiments indicate that the most optimal mixture, for which the most desirable strength was obtained, is 10% metakaolin and 2% colloidal silica.

Effect of exposure temperatures on chloride penetration resistance of concrete incorporating polypropylene Fibers, silica fume and metakaolin

• The diffusion resistance of silica fume (SF) concrete was 1.4–7.3 less than OPC concrete. • The diffusion resistance of metakaolin (MK) concrete was 1.2–3.9 less than OPC concrete. • The effect of 10% SF on migration resistance was almost similar to that of 15% MK. • Models to predict the service life of RC structures in hot environments were developed. Rapid degradation of reinforced concrete (RC) has become a serious concern due to its reduction of life span and high unexpected maintenance cost. Chloride penetration and subsequent corrosion are the primary causes of such concrete deterioration. This study investigated the effects of polypropylene fibers, metakaolin and silica fume on chloride diffusion and migration resistance of concrete at different exposure temperatures. Eight concrete mixes were prepared using a water/binder ratio of 0.38, cement replacement of 0, 5, 10, and 15 % by either silica fume (SF) or metakaolin (MK) with zero or 0.6 kg/m 3 polypropylene fibers (PPFs). Furthermore, concrete resistance to chloride diffusion at four different exposure temperatures (23, 38, 53 and 68 °C) and chloride migration at 23 °C was evaluated. The results showed that both pozzolanic admixtures, SF and MK, significantly reduced apparent chloride diffusion coefficient (D a ) and chloride migration coefficient (D nssm ). However, PPFs concretes incorporating MK showed inferior chloride diffusion than those containing SF. D a for PPFs concretes incorporating SF and MK were 1.4–7.3 and 1.2–3.9 times less than Type I cement concrete, respectively. While D nssm for PPFs concretes incorporating SF and MK were 1.7–6.3 and 1.5–3.2 times less than Type I cement concrete, respectively. The results also showed that the effect of 15 % MK on D nssm and D a was almost similar to that of 10 % SF. The D a increased slightly at exposure temperatures of 23 and 38 °C. However, at higher exposure temperatures of 53 and 68 °C, a significant increase in D a was noted. Eight models were developed using regression analysis and were validated by comparing the predicted apparent chloride diffusion coefficient values with the measured ones. The validation of the developed models showed that the predicted D a values were within ± 7 % error margin. The developed chloride diffusion models in the current study allow us to predict and quantify the long life of future realizations of RC structures in marine hot environments.

Effects of Cooling Methods on the Properties of Concrete with Metakaolin after Thermal Exposure

Metakaolin (MK) have been used in concrete as supplementary cementitious materials (SCMs) due to their economic and environmental benefits. Consequently, the use of MK in concrete production contributes to the overall reduction of CO2 release in the environment. However, for a sustainable built environment, material resistance to thermal exposure is of concern. Previous research have studied the performance of MK at elevated temperature, but there is little or no literature on the effect of cooling methods on concrete structures with MK subjected to varying temperature. Hence, this research investigates the effects of cooling methods on the properties of concrete incorporating MK after thermal treatment (fire). Raw MK was calcined, ground and analyzed using XRD and XRF. 15%MK were used to replace cement. Concrete properties (crushing resistance, density, compressive strength) for water and air cooling methods were determined and compared to a control pure concrete. The heating temperatures were 200°C, 350 °C, 550 °C and 750 °C respectively. The incorporation of MK improved properties of the hardened concrete. Charts and tables showing the effects of MK on the concrete properties investigated were presented. The minimum strength obtained was 28.09 N/mm2 during water cooling and maximum strength 35.20N/mm2 during air cooling. The most enhancing effect of Mk as a replacement material was observed in all the cooling methods considered. Water cooling method was found to have caused severe strength reduction in the concrete structure. MK concrete performs better than pure concrete under aircooling method after thermal exposure, hence, can be adopted for fire aggressive environment.

Durability Study of Nano Influenced Metakaolin Concrete to Acid Attack

The two most important attributes of concrete are strength and durability. The concrete durability crisis has attracted and compelled engineers to focus on concrete performance. Considerable research and attention go into creating reinforced concrete buildings, which face challenging surroundings and are intended to last for a prolonged period of time with minimal maintenance. To accomplish this requirement, one material that has attracted a lot of attention is Nano material combined with SCM's. The researchers looked at partial cement replacement with Metakaolin levels of 10, 20, and 30% and Nano Silica levels of 1.5, 3.0, and 4.5 percent by weight of cement in this study. W/B ratios of 0.3, 0.35, and 0.4 were used with A/B ratio of 1.75. Cubes were cast for different mix proportions and immersed in 5% concentrated HCl, H₂SO₄, and MgSO₄ solutions for 30, 60, and 90 days. The residual compressive strength obtained after 30, 60, and 90 days of immersion in different acid solutions were compared to controlled concrete. According to ongoing research, concrete prepared with a combination of 10% Metakaolin and 3% Nano silica is the best for achieving the highest durability properties in concrete and improving its performance.