Slag Concrete Research Articles

Suitability of electrochemical test methods for evaluating corrosion of steel in alkali-activated slag concrete

The electrochemical tests commonly used for evaluating reinforcement corrosion in Portland cement-based concrete may not be appropriate for testing alkali-activated slag (AAS) concrete due to its different pore structure and pore solution composition. In this article, corrosion behaviour of the steel bars in 12 AAS concrete mixes with different alkali concentration and modulus of sodium silicate solution was monitored by using gravimetric mass loss measurement. The results obtained from other electrochemical tests were compared to the gravimetric mass loss to determine their suitability for assessing the corrosion of steel in AAS concrete. It was found that only 7.8–28% of the mass loss was accounted for by the macrocell current for AAS concretes, indicating that this type of test underestimates the corrosion of the steel in AAS concrete. The steel bars in the AAS concretes gave a much higher negative half-cell potential value, presumably due to the influence of sulfides. In summary, it has been established that the criteria for assessing the onset and progress of corrosion of steel in Portland cement concrete are not suitable for the same purpose in the range of AAS concretes studied.

Effect of Silica Fume on Steel Slag Concrete

- In India, the production of steel slag is about 12 million tons in the steel industries and we can use in our concrete as a waste material. Concrete is most commonly and widely used building material used in all around the world. Concrete is the mixture of cement, sand, aggregates (fine and coarse), and water. The utilization of concrete is continuously increasing due to which there is a great effect on natural resources. There are many numbers of byproducts (like, steel slag, silica fume, fly ash, etc.) that are produced during the production or the manufacturing of material like steel, silicon metal, etc. In the present study effect of silica fume on steel slag concrete has been carried out on M25 grade of concrete by varying percentage of steel slag i.e. 45%, 50% and 55% and constant value of silica fume i.e. 10%. From the study it has been observed that the compressive strength decreases while increases the percentages of steel slag. Therefore, up to 45% replacement of steel slag with the fine aggregates and 10% replacement of silica fume with cement give best result and after that the strength will decreases.

Recycling Cupola Slag in Concrete as Partial Replacement of Fine Aggregate for Sustainable Construction

Abstract: In the current study an effort has been made to investigate the impact of cupola slag inclusion, on the mechanical and durability properties of concrete. Different percentages (10%, 20%, 30%, 50%, and 80%) of cupola slag were used to substitute fine aggregate and corresponding results have been observed. Also, different mechanical and durability tests were carried out to check the suitability of replacing natural fine aggregate by cupola slag. Compressive strength was found to be increased by cupola slag inclusion up to a percentage replacement of fine aggregates of 30%, after which further cupola slag addition resulted in a loss of strength. For flexural and tensile strength similar trends were observed. On the other hand, as the amount of cupola inclusion increased from 0% to 80%, a decreasing trend in both water penetration depth and water absorption was observed. Likewise, for all the aforementioned criteria a notable improvement in chloride penetration was observed due to the inclusion of cupola slag. The study basically focuses on present concern regarding industrial waste which poses a risk to the environment. Industrial waste has been utilized in a sustainable manner, as it has shown improvement in properties as compared to ordinary concrete mix. Such type of modified concrete can be employed in harsh exposure conditions as can be found from durability tests. The findings of this study show that cupola slag is a sustainable matter that works well as a partial replacement for natural sand.

Experimental Study on the Properties of Mortar and Concrete Made with Tunnel Slag Machine-Made Sand.

Machine-made sand is gradually replacing natural sand to achieve sustainable development. Experimental studies and gray-correlation analysis were used to study the properties of tunnel slag machine-made mortar and concrete. The properties of machine-made mortar with different stone powder content were analyzed through experiments. By analyzing the performance of machine-made sand concrete with equal amounts of cement replaced by stone powder, the optimum replacement ratio is obtained. Gray-correlation analysis was used to compare the degree of influence of fineness modulus and stone powder content on the performance of concrete. Scanning electron microscopy (SEM) and X-ray diffractometry (XRD) were used to analyze the microstructure of tunnel slag sand concrete. The test results showed that the flexural and compressive strengths of the machine-made sand concrete were greater than the standard sand with the same stone powder content. The 28-day flexural and compressive strengths had a maximum difference of more than 30%. The best stone powder content of the machine-made mortar is in the range of 5% to 8%. When the replacement cement content of stone powder is about 6%, the mechanical and working properties of machine-made sand concrete achieve the optimal state. The lower the stone powder content, the closer the mechanical and working properties of machine-made sand concrete and river sand concrete. The correlation between the performance of machine-made sand concrete and fineness modulus is the largest. When the stone powder content is low, it has almost no effect on the compressive strength of concrete. The results point out the direction for the quality control of tunnel slag machine-made sand concrete.

Destructive and Non-Destructive Testing of the Performance of Copper Slag Fiber-Reinforced Concrete.

Concrete technology is adopted worldwide in construction due to its effectiveness, performance, and price benefits. Subsequently, it needs to be an eco-friendly, sustainable, and energy-efficient material. This is achieved by replacing or adding energy-efficient concrete materials from industries, such as ground granulated blast furnace slag, steel slag, fly ash, bottom ash, rice husk ash, etc. Likewise, copper slag is a waste material produced as molten slag from the copper industry, which can be used in concrete production. Copper slag can perform roles similar to pozzolans in the hydration process. This paper extends the comparative study of copper slag concrete with polypropylene fiber (PPF) subjected to destructive and non-destructive testing. Under destructive testing, compressive strength of concrete cubes, compressive strength of mortar cubes, splitting tensile tests on cylindrical specimens, and flexural tests on plain cement concrete were conducted and analysed. Ultrasonic pulse velocity and rebound hammer tests were performed on the samples as per IS13311-Part 1-1992 for non-destructive testing. The 100% replacement of copper slag exhibited a very high workability of 105 mm, while the addition of 0.8% PPF decreased the flowability of the concrete. Hence, the workability of concrete decreases as the fiber content increases. The density of the concrete was found to be increased in the range of 5% to 10%. Furthermore, it was found that, for all volume fractions of fiber, there was no reduction in compressive strength of up to 80% of copper slag concrete compared to control concrete. The 40% copper slag concrete was the best mix proportion for increasing compressive strength. However, for cement mortar applications, 80% copper slag is recommended. The findings of non-destructive testing show that, except for 100% copper slag, all mixes were of good quality compared to other mixes. Linear relationships were developed to predict compressive strength from UPV and rebound hammer test values. This relationship shows better prediction among dependent and independent values. It is concluded that copper slag has a pozzolanic composition, and is compatible with PPF, resulting in good mechanical characteristics.

Soft computing models to predict the compressive strength of GGBS/FA- geopolymer concrete

A variety of ashes used as the binder in geopolymer concrete such as fly ash (FA), ground granulated blast furnace slag (GGBS), rice husk ash (RHA), metakaolin (MK), palm oil fuel ash (POFA), and so on, among of them the FA was commonly used to produce geopolymer concrete. However, one of the drawbacks of using FA as a main binder in geopolymer concrete is that it needs heat curing to cure the concrete specimens, which lead to restriction of using geopolymer concrete in site projects; therefore, GGBS was used as a replacement for FA with different percentages to tackle this problem. In this study, Artificial Neural Network (ANN), M5P-Tree (M5P), Linear Regression (LR), and Multi-logistic regression (MLR) models were used to develop the predictive models for predicting the compressive strength of blended ground granulated blast furnace slag and fly ash based-geopolymer concrete (GGBS/FA-GPC). A comprehensive dataset consists of 220 samples collected in several academic research studies and analyzed to develop the models. In the modeling process, for the first time, eleven effective variable parameters on the compressive strength of the GGBS/FA-GPC, including the Activated alkaline solution to binder ratio (l/b), FA content, SiO2/Al2O3 (Si/Al) of FA, GGBS content, SiO2/CaO (Si/Ca) of GGBS, fine (F) and coarse (C) aggregate content, sodium hydroxide (SH) content, sodium silicate (SS) content, (SS/SH) and molarity (M) were considered as the modeling input parameters. Various statistical assessments such as Root Mean Squared Error (RMSE), Mean Absolute Error (MAE), Scatter Index (SI), OBJ value, and the Coefficient of determination (R2) were used to evaluate the efficiency of the developed models. The results indicated that the ANN model better predicted the compressive strength of GGBS/FA-GPC mixtures compared to the other models. Moreover, the sensitivity analysis demonstrated that the alkaline liquid to binder ratio, fly ash content, molarity, and sodium silicate content are the most affecting parameter for estimating the compressive strength of the GGBS/FA-GPC.

Predicting the compressive strength of steelmaking slag concrete with machine learning – Considerations on developing a mix design tool

Steelmaking slag has been extensively studied as aggregate for cement-based composites. Because of the distinct properties of this residue, traditional mix design methods are not suitable to determine its target compressive strength, which hinders research studies and compromises its use on a large scale. In this context, the present work aims to develop machine learning (ML)-based models to predict the compressive strength of steel slag concretes from their mix proportion. For this purpose, a global data survey on steel slag concretes was carried out to create a benchmark dataset. Then, four ML-based models were trained and cross-validated using this dataset: Support Vector Regression (SVR), Artificial Neural Networks (ANN), Extreme Gradient Boost (XGBoost), and Gaussian Process Regression (GPR). Finally, new steel slag concrete specimens were built and tested to experimentally validate the adjusted models. The model that achieved the best performance using the literature dataset was the ANN, with a R2 of 0.79. However, the experimental validation was not satisfactory – the GPR, XGBoost and SVR models presented negative R2 values. These results brought light to some pivotal aspects that must be considered when using ML techniques: i) the size and homogeneity of the dataset; ii) the proper choice of input parameters; and iii) the use of cross-validation to adjust the models. Hence, although such techniques are promising and powerful, care must be taken on the generalization of their predictions, especially when the available data is limited.

Extension of the fib MC 2010 for basic and drying shrinkage of alkali‐activated slag concretes

AbstractAlkali‐activated slag is an alternative to ordinary Portland cement that has been studied for the past 20 years. One of the main challenges for its practical use is understanding and controlling its shrinkage behavior. In this study, new experimental results for two alkali‐activated slag concrete mixes are presented under both sealed and unsealed conditions. The results show that basic shrinkage increases with increased sodium silicate ratio. Under unsealed conditions, the age to exposure to drying has a most significant impact on the final drying shrinkage. Finally, the mechanisms explaining shrinkage of such materials are discussed and thefib Model Code 2010 is extended for alkali‐activated slag concrete using the new experimental results. The extended model consists of four parameters influencing the final values and the speed of both basic shrinkage and drying shrinkage. It is extensively compared with experimental datasets from the literature and improves significantly predictions compared with the original models for both basic and drying shrinkage. This demonstrates clearly the feasibility to extend it for predicting shrinkage of alkali‐activated slag concrete.

Chloride induced corrosion of steel reinforcement in alkali activated slag concretes: A critical review

Alkali activated materials (AAMs) have been recognised as potential alternatives to Portland cement concretes in specific applications in the construction industry due to their environmental benefits such as substantially reduced CO2 emissions and utilisation of industrial wastes. While many studies reported the superior performance of AAM concretes over Portland cement concretes in protecting steel from corrosion, some other studies indicated an opposite view. Hence, there is a need for further research on the long-term corrosion studies of AAM concretes in the laboratory as well as in the field. Among many important areas of investigation is the resistance of AAMs to chloride induced corrosion of steel reinforcement which is not well understood. In this paper, the above aspect is reviewed including chloride ingress, chloride binding and chloride induced corrosion rate of steel reinforcement in AAMs. Chloride ingress in AAMs involves both open and closed pore systems. Chloride binding in AAMs is predominantly physical and not chemical. The chloride threshold levels initiating steel corrosion in AAMs are significantly different in comparison to Portland cement concretes.

Frost Resistance of Alkali-Activated Combined Slag and Fly Ash Concrete Cured at Ambient Temperature

Frost Resistance of Alkali-Activated Combined Slag and Fly Ash Concrete Cured at Ambient Temperature

Shrinkage of Alkali-Activated Combined Slag and Fly Ash Concrete Cured at Ambient Temperature

First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address

Cracking resistance and sustainability assessment of alkali-activated slag concrete incorporating lightweight aggregate

This study aims to evaluate the cracking resistance and sustainability performance of alkali-activated slag (AAS) concretes incorporating pre-wetted lightweight aggregates (LWAs). Three replacement rates (0, 50%, and 100%) of natural coarse aggregates (NAs) with pre-wetted LWAs are used, while the ordinary Portland cement (OPC) concrete alternatives are considered as control samples. The results showed that incorporating pre-wetted LWAs effectively improved the cracking resistance of the AAS concretes, and the effect was more evident as the LWA contents increased. The cracking age of the AAS concretes was delayed from 5.6 d to 8.9 d and 10.6 d with 50% and 100% replacement of NAs by LWAs, respectively. Meanwhile, a desirable result was that the AAS concretes could still endure relatively high tensile stress after the initial cracking. The larger tensile stress could be undertook with the increase in LWA contents. Although the incorporation of LWA slightly increased the environmental burdens of the concrete alternatives, the energy consumption and five environmental impact categories of the AAS concretes were reduced by more than 20% and 40%, respectively, compared to those of OPC concretes with the same LWA content. Similar results were found in the calculation of life-cycle cost. Even for the AAS concretes with 100% LWA content, the significant environmental and economic benefits were still obviously obtained compared to the OPC concretes without LWA.

Production of evaporation suppression floating covers using ultra-lightweight alkali-activated slag concrete

Evaporative losses from reservoirs exacerbate water shortage during dry spells. Notwithstanding the extensive application of self-assembling floating covers for suppressing evaporation, the cover material is often overlooked and limited to available choices such as plastics. The present study is aimed at the production of floating covers using ultra-lightweight alkali-activated slag concrete that offers a range of mechanical and chemical features. Concrete specimens were made with different percentages of ground granulated blast-furnace slag as the binder, sodium metasilicate as the alkaline activator and lightweight perlite aggregates with a density of 100–150 kg/m3. To solve the problem of fracture in the preliminary specimens, slag was partially replaced with 15, 20 and 30% lime. In addition, microsilica (10, 12 and 15%) was introduced to improve the mechanical properties of the samples. In designs without microsilica, 30% replacement of slag with lime resulted in the desirable density, strength and permeability of samples. Results showed that microsilica generally increased the density, resistance and thermal conductivity of samples by 7, 74 and 14%, respectively, while water absorption and permeability decreased by 15% and 14%, respectively. The dry density of samples was obtained between 340 and 516 kg/m3 with a compressive strength of 0.2–0.9 MPa and a conductive heat transfer coefficient of 0.067–0.093 W/mK.

Effect of fillers on the mechanical properties and durability of steel slag concrete

Using steel slag to replace natural coarse and/or fine aggregates to make concrete provides a multi-win solution in mitigating the environmental problems regarding huge depletion of natural aggregates and disposal of large amount of slag. On the other hand, the use of pozzolanic fillers, such as fly ash (FA) and silica fume (SF) could significantly improve the strength, stiffness and durability of concrete. However, there were very few research studies on the effect of pozzolanic fillers on the mechanical behaviour and durability of concrete containing steel slag. To fill up this research gap and promote the use of steel slag, a systematic and scientific experimental study was conducted, in which 29 concrete mixes with steel slag partially or totally replacing natural aggregates and FA/SF partially replacing cement in an equal volume were prepared. The slump, wet packing density (WPD), 7-, 28-, 91- and 182-day compressive strength and durability in terms of total charge passed and chloride ion’s penetration depth in rapid chloride permeability test were tested for all the specimens while the chemical composition of concrete were tested using X-ray diffraction. Test results revealed that the slump of steel slag concrete decreased due to the porous structure of slag. Besides, the use of steel slag improved the compressive strength of concrete. By adding SF to replace partial cement, the strength of steel slag concrete could be escalated further. At given composition of aggregates and filler type, the total charge passed and the chloride ion’s penetration depth of steel slag concrete decreased as the WPD increased due to the denser and impermeable microstructure of concrete that enhanced the resistance of chloride ion penetrability.

A study on the change in frost resistance and pore structure of concrete containing blast furnace slag under the carbonation conditions

In this study, the change in frost resistance and pore structure of concrete containing blast furnace slag with various replacement ratio due to carbonation were investigated. As a result, there is a close relationship between the carbonation speed and 28-day compressive strength in blast furnace slag concrete. The frost resistance, carbonation resistance and scaling resistance of blast furnace slag cement concrete decrease as blast furnace slag replacement ratio increases. Furthermore, due to carbonation, the frost durability of ordinary Portland cement concrete and the concrete with a low replacement ratio of blast furnace slag tends to decrease. However, the concrete with a high replacement ratio of blast furnace slag tends to increase. Under the carbonation conditions, the pore volume decreases due to carbonation of calcium hydroxide, and the pore structure will be coarsened due to carbonation of C-S-H. In addition, it is expected that permeability of concrete is raised and scaling is inhibited due to carbonation, and the surface area with a certain thickness in the carbonated concrete will be scaled due to freeze–thaw.

Drying shrinkage of one-part alkali-activated slag concrete

The aim of this study was to evaluate the drying shrinkage of one-part alkali-activated slag concrete (AASC) for up to 180 days that is influenced by mix design parameters. A total of 24 mix designs for AASC and one for OPC concrete were made and cured in two different environments. The impacts of mix design parameters including water to binder ratio, silica fume to binder ratio, alkaline activator to slag ratio, and two curing regimes, in water and sealed plastic bag, on drying shrinkage were investigated, using experimental tests and SEM analysis. The results showed nearly 75% of the 180-day shrinkage was reached within 20 days. The results also revealed that the addition of silica fume considerably reduced drying shrinkage magnitude. AASC samples cured in sealed plastic bags resulted in at least a 5.9% increase in drying shrinkage. The maximum drying shrinkage was observed in a mix design containing the highest water to binder ratio and zero silica fume content regardless of curing type. The results indicated that the application of silica fume as a co-binder led to a considerable reduction in the drying shrinkage.

Hydration and Microstructure of High-Volume Ground Granulated Blast Furnace Slag Concrete Incorporating Metakaolin

In order to relieve the carbon emission of concrete industry, the application of high-volume ground granulated blast furnace slag (HVGGBFS) concrete is one of low cost and effective methods, but its properties develop slowly which needs to be solved. The impact of metakaolin (MK) on the microstructure and hydration evolution of HVGGBFS concrete has been investigated through the compressive strengths, non-evaporable water, morphology and nanoindentation. The results show that the non-evaporable water evolution of HVGGBFS concrete with MK has a similar trend with the compressive strength evolution. The use of 10% MK increases the compressive strengths of HVGGBFS concrete, and from the beginning of 28 days, its strengths are higher than those of the control concrete without GGBFS and MK. The use of 10% MK replacing cement reduces pores and unhydrated particles of HVGGBFS concrete, and however, increases high density calcium-silicate-hydrate (HD C–S–H) and ultra-high density C–S–H (UHD C–S–H), which may be attributed to C–S–H generated by the pozzolanic reaction of MK largely being HD C–S–H and UHD C–S–H.

Stress evolution in restrained GGBFS concrete due to autogenous deformation: bayesian optimization of aging creep

Stress evolution of restrained concrete is a significant direct index in early-age cracking (EAC) analysis of concrete. This study presents experiments and numerical modelling of the early-age stress evolution of Ground granulated blast furnace slag (GGBFS) concrete, considering the development of autogenous deformation and creep. Temperature Stress Testing Machine (TSTM) tests were conducted to obtain the autogenous deformation and stress evolution of restrained GGBFS concrete. By a self-defined material subroutine based on the Rate-type creep law, the FEM model for simulating the stress evolution in TSTM tests was established. By characterizing the creep compliance function with a 13-units continuous Kelvin chain, forward modelling was firstly conducted to predict the stress development. Then inverse modelling was conducted by Bayesian Optimization to efficiently modify the arbitrary assumption of the codes on the aging creep. The major findings of this study are as follows: 1) the high autogenous expansion of GGBFS induces compressive stress at first hours, but its value is low because of high relaxation and low elastic modulus; 2) The codes highly underestimated the early-age creep of GGBFS concrete. They performed well in prediction of stress after 200 h, but showed significant gaps in predictions of early-age stress evolution; 3) The proposed inverse modelling method with Bayesian Optimization can efficiently adjusted the aging terms which produced best modelling results. The adjusted creep compliance function of GGBFS showed a much faster aging speed at early ages than the one proposed by original codes.

Development of drying shrinkage model for alkali-activated slag concrete

The current study aims to develop a drying shrinkage model for alkali-activated slag concrete (AASC). Three water-to-binder (W/B) ratios (0.44, 0.47 and 0.50), two fly ash contents (0 and 25%) and three silica fume contents (0, 5% and 15%) were studied. Slump, compressive strength and the drying shrinkage test lasting for over 300 d were performed. The results showed that: (1) Increasing both the W/B ratio and fly ash content increased the slump of the concrete, while a 5%-10% silica fume had little effect; (2) The compressive strength of the concrete was decreased with increasing both the W/B ratio and fly ash content, while it was improved with the addition of 5% silica fume; (3) Inclusions of fly ash and silica fume contributed to the reduction of the final drying shrinkage; (4) The current prediction models for drying shrinkage behavior of Portland cement-based concrete was not suitable for AASCs. Based on the results, a novel drying shrinkage prediction model with higher reliability for sodium silicate-activated slag-based concrete cured at the standard environment (20 ± 2 °C and RH of 60 ± 5 %) was developed, which is mainly derived from the model of ACI 209. The well-fitted results of this developed model fully indicated the relatively wide applicability of this model. However, given the complexity of the binder composition of AASC, this model still needs to be further upgraded in future.

Effect of Stress–Strength Ratio and Fiber Length on Creep Property of Polypropylene Fiber-Reinforced Alkali-Activated Slag Concrete

Alkali-activated slag (AAS) is an environmentally friendly green cementitious material that can replace ordinary Portland cement (OPC) and has attracted extensive research by scholars all over the world. However, research regarding its creep performance has been lacking, which in turn affects its further application. The creep of alkali-activated slag concrete is large, and fiber addition has been shown to improve this problem. Polypropylene (PP) fiber has good alkali resistance and is economical. This paper studies the effect of the stress–strength ratio and fiber length on the creep property of PP fiber-reinforced alkali-activated slag (FRAAS) concrete. At the stress–strength ratio of 0.15, PP fiber addition is able to greatly reduce the creep of concrete. When the stress–strength ratio increases, the shorter fiber loses the anchoring force and the holes caused by the longer fiber crack. This in turn leads to the deterioration of the inhibition effect on concrete creep. The CEB-FIP 2010 model is highly accurate, but the final value prediction is small. The early prediction value of the GL2000 model is rather large and conservative. The creep coefficient of the prediction model and the measured secant modulus of PP FRAAS concrete with different fiber lengths under different stress–strength ratios may solve the issue of creep prediction.