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• All measured values for dose were reported to be lower than the recommended values. • Fly ash as a concrete additive could increase the activity concentration in concrete. • External radiation doses were noted to be influenced by building properties. • Annual organ effective dose rates varied, with the minimum for ovaries and the maximum for testes. Environmental radioactivity in building materials can pose radiological risks to residents by exposure to the emitted gamma radiation and radon. In this study, we evaluated the radioactivity concentration of 53 raw building material samples (fly ash, cement, sand, and gravel) and estimated the dosimetric quantities in outdoor exposure scenarios for residents. The concentrations ranged from 40.1 to 77.4 Bq kg−1 for 226Ra, 27.4 to 91.7 Bq kg−1 for 232Th, and 253.5 to 956.2 Bq kg−1 for 40K. Annual effective dose and organ annual effective dose, were estimated for outdoor exposure scenarios for residents. Fly ash showed the highest values for these dosimetric quantities, while cement had the lowest. The annual organs effective dose rate was found to be minimum for ovaries and maximum for testes. However, all measured values were reported to be lower than the recommended values set by radiation safety organizations worldwide. External radiation doses were noted to be influenced by factors such as air exchange rate, room dimensions, wall thickness, and the type of concrete mixture used. Considering all the dosimetric quantities, the study concludes that the studied building materials might pose low radiological risks to public health. [ABSTRACT FROM AUTHOR]

The heterogeneous nature of recycled concrete fines (RCFs) complicates their reuse in new concrete mixtures. A possible solution to this challenge involves separating the calcium-rich cement from the quartz aggregates through aqueous carbonation (AC), forming CaCO 3. AC typically requires large solvent volumes and multiple steps, hindering the industrial application of the process. To address these problems, a one-step AC procedure with low water-solid ratios and the addition of 0.2–1.0 wt% of triethanolamine (TEA) was tested to enhance calcium separation from RCFs as CaCO 3. Pre- and post-carbonation analysis with XRF, Q-XRD, TGA, and sieving revealed that the addition of TEA resulted in an approximately twofold increase in calcium precipitation below 63 µm and increased the amount of sequestrated CO 2 by 16–21 %. These findings showcase the feasibility of AC with low water-solid ratios and the addition of TEA as a means to separate calcium from RCF, aiding RCF reuse. [Display omitted] [ABSTRACT FROM AUTHOR]

The use of recycled concrete aggregates for new concrete production is an important avenue to increase the sustainability of concrete. While numerous studies have demonstrated the benefit of nanosilica on recycled aggregate concrete, a connection between the enhanced properties and the properties of the calcium-silicate-hydrates is unproven. Thus, we investigate how nanosilica modifies the distribution of calcium-silicate-hydrates in fine recycled concrete aggregate mortar. Using an interdisciplinary approach of nanomechanical testing, data science, and advanced chemical, microstructural and pore structure characterization, we find that 12 wt.% nanosilica results in a 30.8% increase in the combined relative amount of high-density and ultra-high-density C-S-H, 16.7% reduction in C-S-H gel porosity, 24.4% reduction in total porosity, and 3.9% increase in fracture toughness. [Display omitted] • Fine recycled aggregate concrete was mixed using 4%–12% of colloidal nanosilica. • The fraction of high-density calcium-silicate-hydrates increased significantly. • The C-S-H gel porosity of fine recycled aggregate concrete decreased by 2.9-16.7%. • The fracture toughness increased for a large amount of added colloidal nanosilica. • The porosity of fine recycled aggregate concrete decreased by 4.9-24.4%. [ABSTRACT FROM AUTHOR]

The search for reliable tools to assess potential deleterious reactions in sulfide-bearing aggregates, is driven by recent field structure damage involving such types of aggregates. The paper presents a new test scheme with detailed procedures and limit criteria. Five aggregates, including pyrrhotite-bearing reactive ones (Connecticut and MSK 0.9), an alkali-silica reactive low-sulfur limestone (Spratt), a non-reactive control (PKA), and a low-sulfide aggregate (MSK 0.2), were used to manufacture concrete specimens that were subjected to the proposed test. The limit criterion, based on modulus of elasticity loss (RMoE), effectively distinguishes non-reactive, reactive, and potentially reactive aggregates. The scheme's reliability is validated against an existing protocol involving sulfur determination and mortar bar expansion testing. Four of five aggregates exhibit similar potential sulfide reactivity. Despite excessive mortar bar expansion, MSK 0.2, with traces of pyrrhotite, shows non-reactive behavior in concrete specimens after electrochemical treatment. The proposed test scheme offers a practical and timely tool for assessing sulfide-bearing aggregate reactivity before concrete production. [ABSTRACT FROM AUTHOR]

Premature degradation of concrete, caused by frost damage, has been associated with inadequate transport properties and poor resistance to deicing salt. In this study, transport properties and deicing salt resistance of various kinds of ultrahigh-performance concrete (UHPC) containing Type V portland cement, fly ash, and microsilica were investigated. Seven combinations of cementitious materials (one reference, three binary, and three ternary) were used to batch UHPCs using a water-to-cementitious material ratio (w/cm) of 0.21. The aggregate-to-cementitious material ratio (Va/Vcm) of 1.20 was kept constant for all mixtures. The investigated transport properties included water absorption, volume of permeable voids, water penetration, rapid chloride penetration, and surface resistivity. The transport properties of the plain UHPCs were also compared to those of the corresponding steel fiber–reinforced UHPCs. The test results showed that the transport properties and deicing salt resistance of the studied binary and ternary UHPCs improved with the inclusion and increases in microsilica, replacing a portion of cement. The addition of steel fiber had a minor effect on strength and transport properties and a moderate increase in deicing salt resistance of the studied UHPCs. While rapid chloride penetration and surface resistivity tests were found appropriate to assess chloride transport through the studied plain UHPCs, both tests were deemed unsuitable for the companion steel fiber–reinforced UHPCs. [ABSTRACT FROM AUTHOR]

The extreme demand for aggregate leads to the exploitation of riverbeds for fine aggregates, affecting the environment adversely. Therefore, a suitable alternative to natural river sand is essentially required. This study focuses on preventing environmental impact by developing polycarboxylate ether (PCE) sand to replace natural river sand (NRS). Development of polycarboxylate ether (PCE) sand by mixing high-volume fly ash, bottom ash, cement, natural river sand, and locally purchased high-solid-content polycarboxylate ether–based superplasticizer (HSPCE). All the physical and chemical properties of PCE sand were observed and satisfied the requirement of current standards. PCE sand yields a good specific gravity of 2.31 and is classified as Zone I sand with a satisfactory friction angle (37°) compared with NRS and geopolymer fly ash sand (GFS). Although the water absorption (6.83%) and pH (12.18) are slightly more than those of GFS and NRS, the alkali silica reaction and soundness are well within the permissible limit as per Indian standards. The chemical analysis by X-ray fluorescence showed the presence of high amounts of SiO2 and Al2O3 with magnitudes of 58.879%, and 26.77%, respectively. Finally, the compressive strength of M25 grade concrete using PCE sand and GFS was observed to be 87.51% and 83.82% with respect to NRS after 28 days, respectively. The results of this study indicate that PCE sand can be a good alternative to NRS for construction work because it not only reduces the environmental effect due to sand mining but also focuses on utilizing fly ash and bottom ash. [ABSTRACT FROM AUTHOR]

The abundant natural volcanic ash (NVA) in East Africa is a prospective supplementary cementitious material that may be used to produce green and economical railway concrete. To mitigate the shrinkage of concrete with NVA, internal curing using a superabsorbent polymer (SAP) is employed in this study. The compressive strength, autogenous shrinkage, and drying shrinkage of internally cured concrete with NVA were measured. In addition, the water loss and internal relative humidity of internally cured concrete with NVA were analyzed. The results indicate that the compressive strength of concrete with NVA shows a linear decreasing trend with SAP. In addition, SAP significantly reduces the autogenous shrinkage but slightly increases the drying shrinkage of concrete with NVA. The internal curing using SAP increases the water loss of concrete, whereas the water released from SAP still significantly improves the internal relative humidity (IRH) of concrete. The positive influence of internal curing on the autogenous shrinkage overwhelms the unexpected influence on the drying shrinkage, resulting in the mitigated shrinkage of concrete with NVA. [ABSTRACT FROM AUTHOR]

By considering the current global challenges such as greenhouse gas emission and waste disposal management, the exploration of geopolymer concrete is highly focused now-a-days. On the other hand, the use of costlier commercial activators acted as the major drawback for the practical existence. Although the recent geopolymer researchers suggested the use of alternative activators from various resources such as palm oil ash, olive ash etc, the application of which are not appreciably promoted due to the complex derivation process. To overcome these effects, in this paper, first time, an attempt is initiated to develop a cost-effective geopolymer concrete by using textile mercerizing water as an alternate activator system. The viability of using mercerizing water instead of commercial sodium hydroxide activator was studied initially. By conducting the pH electrode test and Infrared Analysis, the alkalinity and the presence of sodium metal cations responsible for the reaction kinematics were confirmed. Also, the molar concentration of sodium cations in the mercerizing water was quantified using chemical titration analysis. The feasibility of using mercerizing water in the preparation of geopolymer was assessed using workability, mechanical strength and sustainability. From the results, it was inferred that the developed geopolymer concrete with 100 % textile mercerizing water exhibited the maximum strength of 46.9 MPa, 5.16 MPa and 5.81 MPa respectively under compression, tension and flexure which are almost equivalent and slightly better than the control geopolymer concrete. Also, the developed geopolymer concrete using 100 % textile mercerizing water and the combined flyash-GGBS binder system showcases the highest post-fire residual strength and 48 % reduced water absorption. The cost of construction of geopolymer concrete was significantly reduced by 58.43 % and showed 10.28 % reduced carbon footprint due to the complete replacement of sodium hydroxide solution using textile mercerizing water. The findings of this research work will lead to the development of equivalent molar sustainable activator from the textile mercerizing water and the exploration of eco-friendly and durable geopolymer concrete in an affordable price. [Display omitted] • TMW waste as a 100 % alternative to commercial hydroxide activator. • Alkalinity and reactive metal ions of TMW induced the maximum strength of 46.9 MPa. • GF-TM100 % offered 48 % reduced rate of water absorption and better fire resistance. • Consumption of TMW showed 10.28 % lower carbon footprint than commercial activator. • 58.43 % reduced construction cost in GF-TM100 % geopolymer. [ABSTRACT FROM AUTHOR]

By crushing the prepared cement paste, the recycled powder (RP) was prepared by grinding. The study systematically investigated the effects of microwave power and activation time on the activity of RP. The results showed that the maximum enhancement in the activity of RP occurs when the microwave power is set to 490 W and the activation time is 10 minutes, with the activity increased by 14 %, 15 %, and 22 % at 3, 7, and 28 days, respectively. After microwave activation of RP, the decomposition of C-(A)-S-H and ettringite in the RP provides calcium, silicon, and aluminum phases, and the evaporation of bound water promotes the secondary hydration of RP. After microwave activation, the content of calcium oxide (CaO) in the RP increases, while the contents of silicon dioxide (SiO 2) and alumina oxide (Al 2 O 3) decrease; Adding activated RP to prepare mortar generates more hydration products to fill the pores, making the structure more compact. Compared with the control group, the porosity of the MRP-5 group decreased by 2.38 %. • Studied the effect of microwave excitation on the activity of recycled powder. • The mechanism of microwave-induced recycled powder has been revealed. [ABSTRACT FROM AUTHOR]

Recycled Concrete Aggregate (RCA), derived from discarded concrete, substitutes or stabilizes Natural Concrete Aggregate (NCA) in constructing Recycled Aggregate Concrete (RAC). This study investigates Coconut Shell Biochar (CSB) as a potential mitigator of Alkali-Silica Reaction (ASR) in RAC, particularly in tropical regions like Sri Lanka. CSB, noted for its cost-effectiveness, undergoes assessment for its impact on concrete properties. Petrographic analyses, encompassing optical microscopy and SEM, conducted on CSB-modified RAC in Sri Lanka, reveal favorable mechanical outcomes. Grade 25 RAC, supplemented with CSB, demonstrates 28-day compressive, split-tensile, and flexural strengths of 25.4, 2.5, and 4.1 MPa, respectively. Results indicate CSB effectively alleviates ASR-induced alterations and chemical reactions in RAC, prompting further exploration of CSB's role in controlling specific precipitates and chemical reactions associated with ASR. • There is a demand for recycled aggregate concrete free from alkali Silica reactants. • A need for sustainable solution for alkali silica reaction in recycled aggregate concrete exist. • Petrographic studies show the fractured nature of recycled concrete aggregate. • Coconut shell biochar can reduce secondary alterations and chemical reactions by adsorption. • Finer-size particles of biochar have a high potential for adsorbing secondary materials. [ABSTRACT FROM AUTHOR]