•We compare chloride permeability tests for alkali-activated concrete.•High pore solution conductivity causes problems with electrical methods.•Resistivity and RCPT work but classifications should be ...changed.
This paper presents the results of an experimental study of chloride permeability in alkali-activated fly ash, alkali-activated slag, and Portland cement concrete. Test methods include the rapid chloride permeability test (RCPT), AC and DC electrical resistivity, and the 90-day salt ponding test. We hypothesize that differences in pore solution chemistry between alkali-activated and Portland cement binders render electrical methods unable to accurately estimate chloride permeability in alkali-activated concrete. The present study seeks to evaluate this hypothesis by comparing results from electrical tests with diffusion coefficients from salt ponding tests. Contrary to previous claims, the RCPT provided a good estimate of chloride permeability in both alkali-activated slag and alkali-activated fly ash concrete. RCPT results showed excellent correlation with diffusion coefficients determined from salt ponding tests. Resistivity-measurements exhibited poor correlation to diffusion coefficients and overestimated the resistance to chloride ion penetration. Furthermore, AC and DC resistivity measurements showed significant disagreement for alkali-activated concrete. Finally, evidence form salt ponding tests suggests differences in chloride binding potential between alkali-activated and Portland cement concretes.
In past decades, researchers have tried to improve the durability of concrete by integrating supplementary cementitious materials into concrete. Recent advancements in the field of nano-engineered ...concrete have reported that nanomaterials significantly improve the mechanical and durability properties of concrete. This paper provides a comprehensive summary of recent developments on the use of nanomaterials as a performance enhancer in cement/geopolymer concrete. Many significant correlations associated with the reinforcement of cementitious matrices using nano-TiO2, nano-Fe2O3, nanoclay/metakaolin, and nano-CaCO3 were studied. Performance aspects such as fresh properties, microstructure, mechanical and durability characteristics, and the influence of various particle sizes have been reviewed. The findings from this review confirm the feasibility of using the nanomaterials in cement concrete, with the required properties of building materials. It is also expected that this review provides better insight into using nanomaterials in concrete for the benefit of academic and fundamental research and promotes its practical application in the construction industry.
•NO2 sequestration by the waste concrete was investigated at temperatures relevant to cement kilns flue gas exhaust.•Our study found that waste concrete can be utilized for NO2 mitigation in a cheap ...and sustainable manner.•XRD, TGA, DRIFTS, and BET results allowed us to propose a new mechanism for NO2 interactions with concrete surfaces.
Removing NO2 from cement kilns can have tremendously beneficial effects on the environment and human health. Sequestering NO2 in demolished concrete is an innovative, cost-effective, and sustainable approach to remove NO2 flue-gas from cement kilns and other industrial plants to minimize their environmental impact. Another notable advantage of this approach was signified by our recent discovery of NO2 sequestered Recycled Concrete Aggregate (NRCA) acting as a corrosion inhibitor when recycled backed into new concrete. This paper focuses on NO2 sequestration by the waste concrete at elevated temperatures that are representative of those found in the cement kilns flue gas exhaust. The gas-phase uptake experiments were performed for 1, 2, and 20-years old concrete samples to reflect the variable age of NRCA. The mechanistic studies of NO2 adsorption to concrete surfaces at 27 °C, 150 °C, and 250 °C temperatures that simulate flue gas temperatures were obtained by time-resolved Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTs) and gas-phase analysis. The results showed that NO2 sequestration increased with an increase in temperature. Most importantly, the 20-year-old concrete still had significant uptake capacity, which shows that aged waste concrete can be used to reduce air pollution and then recycled back into new concrete structures to prevent corrosion. These findings were also supported by TGA, BET, and XRD results. The XRD data indicated a presence of alite, belite, ettringite, portlandite, and dolomite, where the increased fractions of portlandite and hydrates were correlated to higher NO2 uptake. Moreover, the BET results indicated notable changes in the microstructure of the concrete at elevated temperatures, which also contributed to changes in the NO2 uptake capacity of concrete.
This paper aims to provide a comprehensive review of recent trends in incorporating biomass ashes from agricultural waste in Ordinary Portland cement (OPC) and geopolymer concrete. The material ...properties of different biomass ashes and their effect on fresh and hardened concrete properties (i.e., mechanical and durability properties) are reviewed. Partial replacement of OPC with byproducts, such as bamboo leaf ash, date palm ash, elephant leaf ash, banana leaf ash and plantain peel ash, rice straw ash, olive waste ash, wheat straw ash, and corn cob ash, escorts reduction in carbon dioxide (CO2) emissions and global warming. It will also contribute to the effort of achieving zero-waste technology and sustainable development.
This paper provides essential background information on the global status, composition, and ash preparation procedures of green and sustainable cementitious materials and then explores their potential applications. This review also highlights the areas requiring further research and indicates the possible negative impacts of utilizing these non-traditional supplementary cementitious materials (SCMs). The findings from this review confirm the feasibility of using biomass ashes as pozzolanic materials in cement concrete or as alternative activators in geopolymer concrete, with the required properties of building materials. Also, it is expected that this review will provide a better insight into biomass ashes incorporated in concrete for the benefit of academic/fundamental research and the construction industry.
•Reviews the utilization of agricultural farming waste ashes as SCMs.•100 literatures were extensively reviewed.•Essential information including global status, composition and preparation procedures.•Explores the potential application as a green and sustainable cementitious material.•Findings confirmed the feasibility of biomass ashes in cement/geopolymer concrete.
The utilization of recycled concrete as an adsorbent to sequester NO2 without additives or catalysts is an innovative, cost-effective, and sustainable approach to capture NO2 from targeted industrial ...facilities. This paper presents the mechanical and durability performance of ordinary portland cement (OPC) concrete containing NO2 sequestered recycled concrete aggregate (NRCA). NRCA was used as a partial replacement for natural fine aggregate at 20% and 40% rates by volume. The incorporation of NRCA in concrete resulted in increased compressive strength, decreased water-permeable porosity, and reduced chloride ion migration. Moreover, test mixtures comprising 40% NRCA showed a significant chloride binding capacity compared to control concrete mixtures. Furthermore, high replacement rates of NRCA noticeably enhanced the resistance to chloride-induced corrosion of steel in concrete or at least was on par with the performance of a commercially available calcium nitrite-based corrosion inhibitor.
•Effect of NRCAs on chloride diffusion and binding in new OPC concrete.•NRCAs synthesized from 2 and 20-year-old demolished concrete.•NRCAs reduced the chloride penetrability in concrete compared to ...conventional RCAs.•NRCAs increased the chloride binding capacity compared to conventional RCAs.•Chloride binding mechanism in NRCA incorporated concrete.
This study investigates the effect of NO2 sequestered recycled concrete aggregates (NRCA) on chloride ion diffusion and chloride binding capacity of concrete. Two types of NRCAs were used as a partial replacement for natural fine aggregate in fresh OPC mixtures at 20% and 40% replacement levels by volume. Control mixtures with conventional recycled concrete aggregates (RCA) were also evaluated for comparison purposes. The water-permeable porosity, rapid chloride permeability, long-term chloride diffusivity, and chloride binding capacity of the test concrete mixtures were evaluated. Results showed that the presence of NRCA reduced porosity as well as both short-term and long-term chloride ion permeability compared to conventional RCA containing concrete. Most importantly, the addition of NRCAs enhanced the chloride binding capacity of concrete. Thermogravimetric and X-ray diffraction analyses demonstrated increased formation of Friedel’s and Kuzel’s salts in concrete due to the incorporation of NRCA. Based on the test results, a mechanism is proposed for the enhanced chloride resistance in NRCA incorporated concrete.
Concrete is one of the most abundantly produced and commonly used construction materials in the world. The production of cement—the main binder in concrete—is energy-intensive, using roughly ten ...times the national average ratio for energy to gross output of goods and services. Given the high demand for concrete globally and the amount of energy used to produce cement, it is worthwhile to find lower embodied-energy materials to partially replace cement to improve the environmental impacts of concrete without decreasing the concrete performance. One such potential cement replacement is the panel glass found in discarded cathode-ray tubes (CRTs). It is against this backdrop that this study aimed to investigate the technical feasibility and the environmental impacts of using a novel blend of recycled glass and CRT panel glass as pozzolanic material for replacing a portion of ordinary portland cement (OPC) in concrete. Additionally, this study simultaneously looked at the concrete functional performance and environmental impact, and the study was performed at an industrial scale using existing production infrastructure, production volumes, standardized testing, and a life-cycle assessment (LCA) to support the functional testing and environmental impact quantification. Results show that the novel blend of glass met the required performance standards, and when it was blended with cement, the mixture produced concrete with similar or improved functional performance and significantly reduced environmental impacts across all examined impact categories. Future work is needed to examine the additional benefits of diverting CRTs from their current end-of-life pathways and de-risking CRT storage.
Nitrogen oxides (NOx), mainly referring to nitrogen dioxide (NO2) and nitric oxide (NO), are toxic gaseous compounds that have been identified as one of the “criteria air pollutants” by the United ...States Environmental Protection Agency. Not only do these noxious NOx gasses pose a threat to health, but they also contribute to the formation of acid rain, atmospheric particles, eutrophication, and various other toxic substances instigating crucial environmental issues. A great deal of research has been conducted on the photocatalytic abatement of NO2 pollutants using cementitious materials with additives such as TiO2 and ZnO2. Nevertheless, these approaches are typically expensive and can be rather cumbersome due to the necessity of continual inspection of the catalysts for deactivation and poisoning. Alternatively, this study utilizes demolished concrete as an adsorbent to capture NO2 without expensive additives/catalysts to produce NO2 sequestered recycled concrete, and consequently employs it as a constituent in new concrete mixtures. Prior studies demonstrated that NO2 could interact with numerous hydrated and unhydrated cementitious components as well as cement-based materials with different chemical compositions. Hence, demolished concrete–a material with a wide range of variability in parent concrete properties–is an excellent adsorbent for removal of toxic NO2. Demolished concrete that is currently being landfilled on a massive scale can be recycled in a sustainable way as an adsorbent to remove NO2 from flue gas from nearby industrial facilities. Even though recent studies focused on improving the efficiency of NO2 removal by cementitious materials, none of these investigations have studied the fate of NO2 sequestered cement-based materials (NSCM) in real-world concrete applications. Thus, for the first time, this dissertation explores the viability of using NO2 sequestered recycled concrete aggregate (NRCA) as a constituent in new ordinary portland cement (OPC) concrete. This thesis work primarily aims at investigating the performance of NRCA incorporated OPC concrete and seeks to evaluate the hypothesis that NRCA could potentially function as an inhibitor against chloride-induced steel corrosion in concrete. A comprehensive experimental program is devised to assess the effect of NRCA on several key mechanical and durability properties of concrete when it is used to replace natural sand in fresh OPC concrete mixtures. Comparisons are made between the concrete mixtures containing NRCA and traditional recycled concrete aggregate (RCA). Moreover, a commercially available calcium nitrite-based corrosion inhibiting admixture (CI) is also used in parallel with NRCA incorporated concrete. Additionally, this dissertation investigates the feasibility of using recycled concrete powder (RCP), a by-product of the main experimental series, as a cement replacement material in OPC concrete. The performance of RCP is compared to a commercially available limestone filler. The results of this dissertation show that NRCA is a promising constituent material for OPC concrete and the NRCA can act as an inhibitor for chloride-induced steel corrosion. NRCA can release soluble nitrite/nitrate ions into fresh OPC mixtures similar to a CI admixture. The incorporation of NRCA is found to enhance the compressive strength, reduce the porosity, and moderately accelerate the hydration reaction in OPC concrete, unlike traditional RCA. Moreover, the morphologies of the main cementitious hydrated products are modified in the presence of NRCA. The underlying mechanisms of the enhanced macroscale performance of NRCA incorporated concrete are elucidated by the microscale performance. The micromechanical properties of the interfacial transitional zones (ITZs), as well as the hydrated products in both new and old cementitious matrices in NRCA incorporated concrete, are found to be better than those of traditional RCA mixtures. Contrary to conventional RCA, NRCA reduced chloride ion diffusion and increased the chloride binding capacity in OPC concrete. Most importantly, the addition of NRCA delayed the initiation of chloride-induced corrosion and reduced the rate of corrosion once initiated to be on par with commercially available CI admixture. Thin passive films are rapidly formed on the rebar substrates in the presence of NRCA. The incorporation of NRCA visibly reduced the pit formation under accelerated chloride exposure conditions. The age of the parent concrete influenced the mechanical and durability properties of NRCA containing concrete significantly, and this became more pronounced in the case of conventional RCA. The quality of the RCAs used in this study decreased as the age of the parent concrete increased. Nevertheless, the process of NO2 sequestration seemed to be effective in circumventing those inferior properties of the traditional RCA up to a certain extent. It is recommended to decide the optimum NRCA content after a thorough investigation of the parent concrete properties. The results of the secondary experimental investigation of this thesis work revealed that the presence of RCP mainly imposed the dilution effect on the OPC cementitious matrix. Consequently, the addition of RCP lowered the strength, volume stability, resistance to chloride permeability, and resistance to water absorption than control OPC mixtures. However, results suggest that the use of recycled concrete powder as a cement replacement material in concrete can still be a viable option, depending upon the particle size, quality of the parent concrete source as well as the intended use of the RCP incorporated concrete. Overall, the findings of this dissertation significantly contributed to the field of sustainable concrete by providing new paradigms of turning solid waste materials into useful products. The results of this thesis work can be further extended to establish guidelines for the effective use of NRCA in practice.
