Reactive Silica Research Articles

Determination of ASR in Concrete Using Characterization Methods

Basaltic rocks are the main source of local crushed rock aggregate for concrete in their region. Basaltic rocks are also potential rocks for alkali–silica reaction (ASR). ASR is a complex mechanism that deteriorates concrete via creating volumetric expansion over time between the reactive silica in the aggregate and the alkali components in Portland cement. However, due to the multi-scale nature of this long-term phenomenon, understanding its mechanism in concrete structures remains difficult to assess. In this study, the morphology and analytical composition of three groups of concrete prepared with basalt aggregate, basalt aggregate with 20% fly ash substitution of cement, and limestone aggregate were analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX); it was characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and differential thermal analysis (DTA) and compared with the ASR structure. The (Na + K)/Si and Ca/Si ratios in SEM/EDX analysis and the water peaks in FT-IR and TGA analyses will help to determine the footprint of ASR.

Construction potential of rice husk ash as eco-friendly cementitious material in a low-water demand for self-compacting concrete

Self-compacting concrete (SCC) is a special mix design that offers advantages, such as high flowability and better compaction. Combining it with natural pozzolans through partial replacement influences considerably the filling and passing abilities, and segregation resistance, while generating high-strength performance. A low water-to-binder ratio (w/b) leads to a dense, non-porous, and durable SCC, but its desired workability is difficult to obtain. Hence, the addition of chemical admixtures, such as superplasticizers (SP) and air-entraining agents (AEA) may resolve this issue. Moreover, the incorporation of rice husk ash (RHA) as supplementary cementitious material (SCM) in an alkali environment promotes enhanced stability and workability, as well as avoiding any bleeding or segregation problems. RHA also improves the concrete’s microstructure owing to its highly reactive fine silica. However, there is limited evidence reported on the effects of RHA on SCC’s overall flowability, pozzolanic reactions, and microstructural analyses. Here the synergistic effects of RHA on the rheological performance, strength development, pozzolanic activities, and microstructural characterization of fresh and hardened SCC were reported. The study showed that while the filling ability, passing ability, and segregation resistance of fresh mixture all conform to the threshold values, the recorded compressive strength of the hardened samples was highest in SC-09 at 90-day cured samples. The mix proportion of this sample includes a low w/b ratio of 0.35 and 15% RHA replacement, with optimized rheological performance and pozzolanic activities. It was observed in the sample’s microstructure that the silica particles chemically reacted with CH, promoting CSH gel products. The disappearance of dicalcium silicate (C2S) and tricalcium silicate (C3S) in diffractograms was observed and replaced by CSH gel, which plays a key role in strength formation. IR spectral bands at ∼765 and ∼464 cm−1 indicated the amorphous silica phase of the RHA-SCC samples, while the spectral band relation of RHA and the samples showed a high degree of reaction of RHA upon mixing. The surface morphology images proved a highly dense matrix in 15% RHA replacement. Observed pores and cracks were lessen compared to samples with 0–10% RHA, which verified the construction potential of RHA in an optimized amount. While the sulfate and seawater performance tests indicated a low mass loss and high relative strength occurred to samples with 15% RHA replacement when immersed to both solutions, signifying that the addition of RHA in concrete leads to better chemical attack resistance compared to OPC alone due to the highly reactive silica of RHA.

Temporal phytoplankton dynamics and environmental variables in four Ethiopian soda lakes

We investigated the spatio-temporal dynamics of phytoplankton composition, chlorophyll-a as a proxy for algal biomass, and abundance in relation to environmental parameters in four Ethiopian soda lakes: Arenguade, Beseka, Chittu, and Shala. Triplicate water samples were collected from each lake from January to December 2020, four times in different seasons. Lake Chittu had the highest chlorophyll-a concentration, followed by Lake Arenguade, Beseka and Shala. Chlorophyll-a concentrations generally increased during the post rainy and dry season. The results of LR models are high for lakes Arengude, Beseka and Chittu. Lakes Shala and Beseka had the highest number of phytoplankton taxa, with both taxa composition and abundance dominated by Bacillariophyceae. Cyanoprokaryota, particularly Limnospira fusiformis, predominated in the abundance of Lakes Arenguade and Chittu. Water temperature, Secchi depth, turbidity, electrical conductivity, soluble reactive phosphorus, nitrate and silica significantly influenced the phytoplankton community structure. Long-term trend analysis revealed changes in phytoplankton biomass and lake taxonomic composition. The alteration in phytoplankton biomass and species composition of the lakes could be attributed to three factors: (1) frequent high-velocity explosions conducted for seismological studies in the past. This impact caused a dramatic increase in lake level in the case of Lake Beseka leading to a drop in nutrient concentration; (2) climate change and (3) salt content. Overall, our findings suggest that phytoplankton composition, biomass, and abundance varied according to seasonal fluctuations, emphasizing the possible effects of anthropogenic and natural causes on their community structure.

A critical review of experimental research on the durability of cement modified with partial steel slag replacement

The construction industry is looking for sustainable and cost-effective alternatives to conventional building materials. As the world faces increasing environmental challenges, the need for greener construction practices has become more urgent. Cement production is known for its high energy consumption and significant carbon dioxide emissions. Therefore, it is essential to find ways to reduce the environmental impact of cement production and use. One promising area of research is the use of industrial byproducts such as steel slag to partially replace cement in concrete. The use of these by-products not only solves the problem of waste disposal but also provides a sustainable solution to improve the properties of building materials. When mixed with cement, steel slag participates in pozzolanic reactions, in which reactive silica from the slag reacts with calcium hydroxide, produced during the hydration of cement, to form calcium silicate hydrate gel (CSH). This CSH gel is responsible for the strength and durability of concrete. Incorporating steel slag can improve the mechanical properties of concrete, including compressive, flexural, and tensile strength. In addition, steel slag can improve the durability properties of concrete, such as resistance to chemical attack, reduced permeability, and increased resistance to physical and chemical degradation over time. This paper investigates the durability properties of cement when partially replaced by steel slag, focusing on various aspects of durability, including resistance to chemical attack, mechanical strength, and long-term performance under various environmental conditions. The study includes a comprehensive experimental program designed to evaluate the impact of steel slag on the durability of concrete through a series of tests and analyses.

Influence of Si/Al molar ratio and ca content on the performance of fly ash-based geopolymer incorporating waste glass and GGBFS

This study delved into the utilization of waste glass powder (WGP) and ground granulated blast-furnace slag (GGBFS) as a binder and waste glass cullet (WGC) fine aggregate in fly ash (FA) based geopolymer concrete. The inherent characteristics of WGP, WGC, FA and GGBFS can be significantly altered by multiple factors such as sources, combustion temperatures, particle size, and impurity level. To offset the inconsistent characteristics of listed waste materials, this study provides a universal index to quantify and evaluate its reactivity to be used as aluminosilicate precursor and aggregate feedstock Ten distinct groups were examined: in five groups WG replaced fly ash at varying percentages (0, 10, 20, 30, 40%), and in five groups WG was used as a sand substitute with different fly ash and slag ratios (20, 40, 60, 80%). Alkali leaching tests were conducted on WGP, WGC, FA and GGBFS to determine the dissolubility and dissolution rate of reactive silica (Si) and calcium (Ca) within 3 h. The dissolubility and dissolution efficiency demonstrated decent correlations with the mechanical and durability properties of the resultant FA-based geopolymer. Leaching tests demonstrate that Ca from WGP, WGC, FA and GGBFS readily leaches out and reacts in both ambient and oven curing, while Si only exhibits activity primarily in high-temperature environments. Overall, the reactivity of Ca from GGBFS and WG improved by up to 50% and 30% in compressive strength and water absorption, respectively. Moreover, based on alkali leaching test, the most effective molar ratios (Si/Al=3.5–4) demonstrated the highest compressive strength (60–70 MPa), and verified intensively using scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS). Lastly, this study revealed that WGC as fine aggregate with the size of 20 µm also leached out a significant amount of Ca to the geopolymerization process.

Molecular Design of Functional Polymers for Silica Scale Inhibition.

Silica polymerization, which involves the condensation reaction of silicic acid, is a fundamental process with wide-ranging implications in biological systems, material synthesis, and scale formation. The formation of a silica-based scale poses significant technological challenges to energy-efficient operations in various industrial processes, including heat exchangers and water treatment membranes. Despite the common strategy of applying functional polymers for inhibiting silica polymerization, the underlying mechanisms of inhibition remain elusive. In this study, we synthesized a series of nitrogen-containing polymers as silica inhibitors and elucidated the role of their molecular structures in stabilizing silicic acids. Polymers with both charged amine and uncharged amide groups in their backbones exhibit superior inhibition performance, retaining up to 430 ppm of reactive silica intact for 8 h under neutral pH conditions. In contrast, monomers of these amine/amide-containing polymers as well as polymers containing only amine or amide functionalities present insignificant inhibition. Molecular dynamics simulations reveal strong binding between the deprotonated silicic acid and a polymer when the amine groups in the polymer are protonated. Notably, an extended chain conformation of the polymer is crucial to prevent proximity between the interacting monomeric silica species, thereby facilitating effective silica inhibition. Furthermore, the hydrophobic nature of alkyl segments in polymer chains disrupts the hydration shell around the polymer, resulting in enhanced binding with ionized silicic acid precursors compared to monomers. Our findings provide novel mechanistic insights into the stabilization of silicic acids with functional polymers, highlighting the molecular design principles of effective inhibitors for silica polymerization.

Probing surface Earth reactive silica cycling using stable Si isotopes: Mass balance, fluxes, and deep time implications.

Geological reservoir δ30Si values have increasingly been applied as paleoclimate and paleoproductivity proxies. Many of these applications rely on the assumption that the surface Earth Si isotope budget is in mass balance with bulk silicate Earth, such that trends in δ30Si over time can be attributed to changes in flux to or from key silica reservoirs. We compiled δ30Si data from modern reservoirs representing the major sources and sinks of surface Earth reactive silica, to which we applied an inverse model to test assumptions about mass balance. We found that δ30Si values of reverse weathering products must closely match those of diatoms, conflicting with previous assumptions. Model results also revealed that of the 19 to 21 teramoles per year Si released during silicate mineral weathering, ~10 to 18 teramoles per year is stored in terrestrial silica sinks, consistent with assumptions of incongruent weathering reactions. Our results demonstrated that the modern silica cycle summary is in isotopic mass balance.

Algunos aspectos limnológicos abióticos de las cuencas de los ríos Limay y Neuquén con especial referencia al embalse Ramos Mexía

The Negro river tributaries are the Limay and Neuquen rivers, which constitute the Andean eastern drainage system betweem 36" and 41" S. Huge reservoirs have been constructed, as a part of a hydroelectric power program and also for flood control purposes.
 Morphometric and lithological differences accounts for thermal and chemical distinctive fractures between these reservoirs.
 The Ramos Mexía impoundment and Pellegrini off-channel reservoir are wind mixed all over the year, while in the deeper Los Barreales and Mari Menuco stratification develops during the summer.
 The annual heat budget of the Ramos Mexía has been raughly estimated in 36131, 30760 and 31047 cal cm-2 for the years 1978, 1979-1980 and 1980-1981 respectively. These estimates are higher than those for others lakes situated on the Andes mountains in a region of more oceanic climate.
 The waters of the system are well oxygenated, neutral and soft. The Limay basin waters are the more diluted, with an average conductivity of 30 μScm-1 near the glacial lake Nahuel Huapi, and 67 μScm-1 in the Ramos Mexía artificial lake. Conductivity seasonal changes are related with discharge flow rate patterns and with level changes in the reservoirs. The Neuquen basin waters present conductivities ranging from 75 μScm-1 near the Andes, to 250 μScm-1 in Mari Menuco reservoir, while the Pellegrini attains to 3600 μScm-1.
 Both rivers (and R. Mexía artificial lake) have calcium-bicarbonate type waters, beeoming richer in sulphate and sodium as they move seaward through a semiarid region. In Los Barreales and M. Menuco reservoirs bicarbonate and sulphate may change their relative positions during the annual hydrologic cycle. The Pellegrini dosed basin belong to the sulphate-chloride sodium type.
 Reactive silica concentration is rather high throughout the year, without showing depletion to any important extent due to biogenic activity, except in the Pellegrini artificial lake.

Production of sustainable lime-based brick using carbonated recycled concrete fines: Mechanical, mineralogical and microstructure properties

A novel method for reusing construction waste and simultaneously sequestering CO2 in the form of mineral carbon is presented in this study. The method involves the production of construction bricks using waste concrete fines treated with carbonation. Initially, waste concrete is crushed and ground into recycled concrete fines (RCF), which are then subjected to a carbonation process to obtain carbonated recycled concrete fines (CRCF). Comprehensive characterization using XRD, TGA, FTIR, and zeta potential measurements reveals that CRCF exhibits a microstructure featuring silica-coated calcium carbonate particles on its surface, imparting significant reactivity to CRCF. In this investigation, RCF and CRCF are separately mixed with Ca(OH)2, molded, and compressed into bricks, with performance testing conducted under various material ratios and manufacturing conditions. The results indicate that bricks made with CRCF exhibit mechanical properties exceeding those of RCF-based bricks by more than two-fold. This improvement can be attributed to the refined pore structure observed in CRCF bricks. The highly reactive silica gel present on the surface of CRCF reacts with Ca(OH)2 to form C-S-H, providing a rationale for the superior strength displayed by CRCF bricks.

Coal gasification slag-derived highly reactive silica for high modulus sodium silicate synthesis: Process and mechanism

Coal gasification slag (CGS) was used to synthesize highly reactive silica, which can be rapidly dissolved in dilute alkali solution at ambient temperature. High modulus sodium silicate was further synthesized by alkali dissolution at ambient temperature instead of the conventional high temperature melting method. During the acid activation process, the inert Si-O-M (M = Al, Ca, Fe) bonds are broken, resulting in the formation of Q3 and Q2 coordination structures with active Si-O-H bonds. The active Si-O-H bonds are further spontaneously condensed to generate highly reactive amorphous silica with a low Si-O-Si bond strength. Under the optimum reaction temperature of 25℃ and reaction time of 0.5 h, the leaching efficiency of Al, Ca and Fe are 86.20 %, 97.61 % and 97.83 % respectively, and the solubility of silica can reach 97.85 %. During the alkali dissolution of silica process, with the decrease of NaOH concentration and liquid–solid ratio, the breaking of Si-O-Si bridging oxygen bond and the formation of Si-O-Na non-bridging oxygen bond can be decreased, resulting in the direct dissociation of the Si-O groups into the liquid phase in the form of polysilicate, thus synthesizing high modulus sodium silicate. Under the optimum reaction temperature of 25℃ and reaction time of 0.5 h, the leaching efficiency of silica is 76.35 % and the modulus of sodium silicate can reach 3.28. The findings of this study provide valuable insights for enriching the theoretical basis of alkali solution-based silica dissolution and for improving the energy-intensive status of the silica industry.

Valorization of waste concrete powder (WCP) through silica fume incorporation to enhance the reactivity and hydration characteristics

The aim of this study is to utilize the bulk proportion of waste concrete powder (WCP) as cementitious material in the fabrication of binder, and to investigate the impact of silica fume on the reactivity and hydration characteristics of thermomechanical activated WCP. A 29 Silicon Nuclear Magnetic Resonance (NMR) analysis confirmed the presence of reactive silica in the activated WCP. Various blends were prepared with a 50%–80% substitution of type CEM I 52.5 N cement. The combination of activated WCP and silica fume improved the reactivity of the binder blend and achieved a compressive strength comparable to cement. Mineralogical analysis revealed the development of secondary C–S–H gels in mixtures containing silica fumes and activated WCP, which is the result of a secondary hydration reaction between portlandite and reactive silica. The use of life cycle analysis software for the replacement of 60 wt % of cement with activated WCP was found to reduce carbon dioxide emissions by 80.42% due to the use of less cement, an environmentally friendly WCP activation process, even when considering the addition of 10% silica fume. This innovative approach not only enhances WCP reactivity and mechanical strength but also significantly contributes to the reduction of carbon emissions. By elucidating the formation mechanisms and environmental benefits, this study paves the way for a more eco-conscious and efficient construction methodology, promoting the vision of a greener future.

Constructing flame retardant silica nanoparticles through styrene maleic anhydride copolymer grafting for PC/ABS composites

Organic-inorganic hybrid particles have been prepared by grafting styrene maleic anhydride copolymer (SMA) onto reactive amino-modified silica nanoparticles. The SMA modified SiO2 (SMA-SiO2) was incorporated into polycarbonate (PC)/acrylonitrile-butadiene-styrene (ABS) composites (4:1, wt%/wt%) with bisphenol A bis (diphenyl phosphate) (BDP) to simultaneously improve the mechanical properties and flame retardancy. The mechanical properties of the sample containing SMA-SiO2 are apparently improved compared with that of samples containing unmodified SiO2. It is found that SMA-SiO2 tends to distribute at the phase interface of PC/ABS, and therefore improves the compatibility between PC and ABS. Besides, the peak of heat release rate (PHRR) and the total smoke production (TSP) of the PC/ABS composites are decreased by the presence of SMA-SiO2. It is suggested that SMA-SiO2 can form a flame retarding shell at the phase interface to protect ABS. In summary, both the mechanical properties and flame retardancy of PC/ABS composites are significantly improved due to the selective distribution of SMA-SiO2.

Control mechanisms on the reactive silicate fluxes by using on board resuspension experiments in the eutrophicated coastal environment

This study aims to differentiate bio-mediated and biogenic CO3 -2 precipitation or terrestrial CO3 -2 input using onboard incubation techniques, to investigate the effects of resuspension in the coastal environment and to increase our understanding of predicted relationships between silicate releases and other biogeochemical variables in resuspension events. Relationships between dark silicate flux and BSi, CO3 -2, OrgC, Mn (manganese) according to the seasons were examined. The silica flux is controlled by the CaCO3 coating on the diatom skeletons due to the fact that diatom skeletons act as crystallization nuclei in the calcite precipitation that is biologically affected. The reduction in flux with BSi may be due to the reduction in the surface areas of larger diatom species. The negative linear relationships observed between silica fluxes and CO3 -2 is indicative of RSi fluxes constrained by bio-mediated carbonate increase. Linear relationships which are the same in their slopes but differ in their intercepts, reveal the effect of the change in diatom size on silica flux. Smaller diatoms have more surface area per unit volume, meaning an increased silica flux. On the other hand, seeing different CO3 -2 values at stations with the same orgC value have increased the confidence interval (CI) 95% in the linear relationship. The presence of different silica flux values in stations with the same carbonate value may be explained both by different orgC values and by diatoms containing different group sizes. The silica flux is controlled by the CaCO3 coating on the diatom skeletons due to the fact that diatom skeletons act as crystallization nuclei in the calcite precipitation that is biologically affected. The main mechanism controlling the reactive silica flux is carbonate precipitation. The observation of different silica flux values in stations with the same carbonate values can also be explained by OrgC.

Calcium wastes as an additive for a low calcium fly ash geopolymer

A geopolymer is a low-carbon cement based on the utilization of waste ash in alkali-activated conditions. Coal fly ash is widely used as a source material for geopolymer synthesis since it contains a sufficient amount of reactive alumina and silica for geopolymerization. Geopolymer products are known to have beneficial fire resistance and mechanical properties. Class F or low-calcium fly ash (LCFA) is generally used as a primary aluminosilicate source; however, heat curing is required to complete the reaction and hardening process and achieve a strong composite. Furthermore, calcium additives are often required to improve the strength of LCFA geopolymers. This paper presents the potential of reusing calcium waste for this purpose. Three calcium wastes, namely calcium carbide residue (CCR), limestone waste, and waste cement (WC) slurry in powder form were used as additives and compared with the use of ordinary Portland cement (OPC). LCFA was replaced with the calcium additives at 20%. However, 20% CCR resulted in flash setting, hence 5% CCR was used instead. A durability test using 3% HCl solution was also performed. The results showed that the reactivity of calcium additives played an important role in strength development. In the calcium–aluminosilicate–alkali system, calcium silicate hydrate (CSH) and calcium aluminosilicate hydrate (CASH) were formed. The maximum strength of 21.9 MPa was obtained from the OPC/LCFA geopolymer, and 3% HCl solution had a deleterious effect on the strength. OPC and CCR were favorable reactive sources of calcium compounds to blend with LCFA. From the thermogravimetric results, lower thermal weight changes with higher strength gains were achieved. Low CaCO3 decomposition at 750 °C according to the TGA curves indicated the more formation of thermally stable CSH and high compressive strength of Ca/LCFA geopolymers.

A novel combined metallurgy-beneficiation method for the facile and low-cost comprehensive resource utilization of low-grade kaolin solid wastes

Low-grade kaolin is the largest emissions of industrial solid waste that is difficult to dispose of and pollutes the environment seriously. From the perspective of harmless and complete resource utilization, we proposed a novel strategy that combines the wet leaching under mild conditions and physical beneficiation for the facile and low-cost high-valued utilization of low-grade kaolin that involves high-efficiency recovery of aluminum (Al), silicon (Si), and titanium (Ti). The key to successful implementation of this method lies in the new discovery that the residual SiO2 after Al extraction of kaolinite by acid leaching under specific conditions could be rapidly dissolved in dilute NaOH solution at room temperature 25 °C. This highly reactive SiO2 challenges the conventional notions of various silica species are usually chemically stable. By adjusting the key technical parameters of the thermal activation-acid leaching process, the selective and efficient extraction of Al2O3 from low-grade kaolin was realized. The acid leaching residue was then subjected to selective recovery of SiO2 by alkaline leaching at 25 °C to obtain high-quality sodium silicate. Finally, the alkali leaching residue as titanium coarse concentrate was separated by centrifugal concentrator to obtain artificial rutile (TiO2 >91.06%). The key mechanism for the formation of the highly reactive silica was also systematically studied and confirmed.

Relationship between Cyanobacterial Abundance and Physicochemical Variables in the Ebro Basin Reservoirs (Spain)

One of the main problems arising in inland waterbodies is nutrient enrichment that accelerates eutrophication, causing massive cyanobacteria blooms and degrading aquatic ecosystems. This study focused on physical/chemical factors that affect cyanobacteria of 30 reservoirs in the Ebro River basin within the Iberian Peninsula of northeastern Spain. The abundance of cyanobacteria was assessed as total cell number, total biovolume, and the indicator pigment, total phycocyanin (PC). In addition, empirical measurements for PC were compared to PC estimated from remote sensing. Variables assessed for correlation with cyanobacteria abundance included temperature, pH, light availability inferred from Secchi depth, water residence time, total nitrogen, dissolved inorganic nitrogen, total phosphorus, soluble reactive phosphorus, silica, and total phytoplankton biomass as chlorophyll a. These variables were also assessed with a multi-statistical principal component analysis for relationships with cyanobacteria abundance. Cyanobacteria cell number and biovolume were positively correlated with temperature, total nitrogen, total phosphorus, and water residence time, and negatively correlated with silica. High PC concentrations were documented in the reservoirs, and satellite images from remote sensing showed the PC spatial distribution and heterogeneity in the reservoirs. The PCA results show that some variables, such as nitrogen and phosphorus, are closely related to the abundance of cyanobacteria, while other variables such as silica do not show a clear relationship. This study contributes to the knowledge base about inland waterbodies from a physical/chemical perspective, which had not been done before in the Ebro Basin, including the application of analytic tools such as remote sensing.

Experimental investigation on strength, durability and micro structural characteristics of slag based concrete

In this study, experimental investigations are conducted using 100 percent Portland Slag Cement and Processed Granulated Blast Furnace Slag sand (PGBFS, iron slag) with 100 percent and partial or full replacement of Natural Coarse Aggregates (NCA) with Ladle Slag Aggregates (LSA) with 0, 20, 40, 60, 80, and 100 percent variations. All of the materials used in the inquiry are manufactured by Jindal Steel Works' Bellary factory in India. It has been shown that aggregates containing 20 percent Ladle slag provide the highest strength. Again, 5 percent variation strength tests are conducted, and it is determined that maximum strength is attained with 20 percent variance. The XRD examination demonstrates that the intermolecular bonding between hardened aggregate and cementitious paste is mostly comprised of silicates with a high degree of crystalline order. Due to the fact that the XRD test pattern is mostly composed of quartz aligned with alite and belite, the spaces between the substrate have been minimized to a minimal extent, which may contribute to the concrete's excellent endurance. For 20 percent variance, the tests of durability are modest, as shown by the durability test. The SEM images show porous structures which suggest a limited formation of C-S-H, gel and a correlation between them. The calcium hydroxide generated during cement hydration could be the result of interaction with the reactive amorphous silica present in slag and cement, leading to the formation of C-S-H gel, which plays a role in enhancing the mechanical and durability properties of concrete.

Is pulmonary inflammation a valid predictor of particle induced lung pathology? The case of amorphous and crystalline silicas

Although inflammation is a normal and beneficial response, it is also a key event in the pathology of many chronic diseases, including pulmonary and systemic particle-induced disease. In addition, inflammation is now considered as the key response in standard settings for inhaled particles and a critical endpoint in OECD-based sub-acute/ chronic animal inhalation testing protocols. In this paper, we discuss that whilst the role of inflammation in lung disease is undeniable, it is when inflammation deviates from normal parameters that adversity occurs. We introduce the importance of the time course and in particular, the reversibility of inflammation in the progression towards tissue remodelling and neoplastic changes as commonly seen in rat inhalation studies. For this purpose, we used sub-chronic/ chronic studies studies with synthetic amorphous silicas (SAS) and reactive crystalline silica (RCS) as a source of data to describe the time-course of inflammation towards and beyond adversity. Whilst amorphous silicas induce an acute but reversible inflammatory response, only RCS induces a persistent, progressive response after cessation of exposure, resulting in fibrosis and carcinogenicity in rodents and humans. This suggests that the use of inflammation as a fixed endpoint at the cessation of exposure may not be a reliable predictor of particle-induced lung pathology. We therefore suggest extending the current OECD testing guidelines with a recovery period, that allows inflammation to resolve or progress into altered structure and function, such as fibrosis.

Glass powder mortar – A study on alkali-silica reaction and environmental impact

Reuse and recycling of generated waste is a crucial step in achieving sustainability in the construction sector. Among various types of construction and demolition wastes, the amount of waste glass is huge, which can be recycled and reused as a partial substitute of cement. The alkalis present in the cement reacts with reactive silica content in the recycled glass and deteriorates the concrete by undergoing expansion induced by alkali-silica reaction. In this study, alkali-silica reaction of a mortar bar is tested to analyze the effect of glass powder used as a substitute of silica powder. Two different colors of glass powder blue and green were used in the study and compared with the reference mix consisting of silica powder (which is a substitute for cement by 27%). The result shows that on replacing 100% of silica powder by glass powder the expansion induced by alkali-silica reaction reduces. Along with finding the durability properties, the benefits and impacts of waste glass on the environment becomes an important aspect. To understand the consequence of waste glass powder on the environment, life cycle assessment is conducted. The result shows that glass powder has lower environmental impact in comparison with silica powder.

High Performance Concretes with Highly Reactive Rice Husk Ash and Silica Fume.

The search for new sources of high-quality non-crystalline silica as a construction material for high-performance concrete has attracted the interest of researchers for several decades. Numerous investigations have shown that highly reactive silica can be produced from rice husk, an agricultural waste that is abundantly available in the world. Among others, the production of rice husk ash (RHA) by chemical washing with hydrochloric acid prior to the controlled combustion process has been reported to provide higher reactivity because such a process removes alkali metal impurities from RHA and provides an amorphous structure with higher surface area. This paper presents an experimental work in which a highly reactive rice husk ash (TRHA) is prepared and evaluated as a replacement for Portland cement in high-performance concretes. The performance of RHA and TRHA was compared with that of conventional silica fume (SF). Experimental results showed that the increase in compressive strength of concrete with TRHA was clearly observed at all ages, generally higher than 20% of the strength obtained with the control concrete. The increase in flexural strength was even more significant, showing that concrete with RHA, TRHA and SF increased by 20%, 46%, and 36%, respectively. Some synergistic effect was observed when polyethylene-polypropylene fiber was used for concrete with TRHA and SF. The chloride ion penetration results also indicated that the use of TRHA had similar performance compared to that of SF. Based on the results of statistical analysis, the performance of TRHA is found to be identical to that of SF. The use of TRHA should be further promoted considering the economic and environmental impact that will be achieved by utilizing agricultural waste.