Effect of Nano Alumina on Compressive Strength and Microstructure of High Volume Slag and Slag-Fly Ash Blended Pastes

This paper presents the effect of nano alumina (NA) on compressive strength and microstructure of cement paste containing high volume blast furnace slag (HVBFS) contents of 70, 80, and 90% as partial replacement of cement and combined blast furnace slag (BFS) and class F fly ash (FA) contents of 70 and 80% as partial replacement of cement. FA is used at 30% as partial replacement of BFS. NA contents are varied from 1 to 4% as partial replacement of BFS and BFS-FA. Results show that the addition of NA improves the compressive strength of high volume BFS and BFS-FA pastes by 2 to 16%. The compressive strength of paste containing 69% BFS, 30% cement, and 1% NA exceeded the compressive strength of control cement paste while the compressive strength of paste containing 77% BFS, 20% cement, and 3% NA is 1% lower than control cement paste. NA significantly reduced the large capillary pores of >0.1 microns of high volume BFS and BFS-FA pastes. No evidence of reduction of Ca(OH)2 in high volume BFS pastes is observed due to addition of NA, however, in high volume BFS-FA paste the Ca(OH)2 is reduced due to addition of NA. Increase in intensity peaks of CAH, Ettringite and CSH in X-ray diffraction analysis is observed in high volume BFS and BFS-FA pastes due to addition of NA, which coincides with the observed more dense microstructure of high volume BFS and BFS-FA pastes containing NA than those without NA

Mechanical and durability properties of C–S–H-seeded cement mortar cured at fluctuating low temperatures with granulated blast furnace slag as fine aggregates

AbstractThe conservation of natural resources, efficient use of industrial side-streams, and reduction of environmental impacts are the main targets of the construction sector worldwide. However, the low ambient temperatures and long harsh winter seasons in northern regions limit the use of industrial side-streams in construction activities under cold weather conditions due to their slow strength development rate. This study aimed to develop an eco-friendly construction material suitable for construction under cold weather conditions using blast furnace slag as a binder and fine aggregate admixed with a calcium silicate hydrate seed accelerator in mortar. Natural sand (NS) was volumetrically substituted with 25%, 50%, 75%, and 100% of granulated blast furnace slag (GBFS) fine aggregate in mortar cured at fluctuating low/freezing temperatures (+5 to −5 °C), representing the late fall and early spring seasons in northern regions. The mortar’s compressive strength increased with the incorporation of GBFS aggregate over the first three days of curing and decreased thereafter. A denser interfacial transition zone was captured around GBFS aggregates than NS in the three days old mortars. The deceleration influences of fluctuating low/freezing temperatures on the compressive strength development of mortars were diminished with time. Capillary water absorption increased with higher GBFS aggregate contents. Mortar with 25–50 vol.% GBFS aggregates exhibited greater frost resistance than control mortar with NS only. The incorporation of GBFS aggregate enhanced the mortar’s resistance against a sulfuric acid attack. This study demonstrates the potential of GBFS aggregate for use in construction under cold weather conditions.Abstract The conservation of natural resources, efficient use of industrial side-streams, and reduction of environmental impacts are the main targets of the construction sector worldwide. However, the low ambient temperatures and long harsh winter seasons in northern regions limit the use of industrial side-streams in construction activities under cold weather conditions due to their slow strength development rate. This study aimed to develop an eco-friendly construction material suitable for construction under cold weather conditions using blast furnace slag as a binder and fine aggregate admixed with a calcium silicate hydrate seed accelerator in mortar. Natural sand (NS) was volumetrically substituted with 25%, 50%, 75%, and 100% of granulated blast furnace slag (GBFS) fine aggregate in mortar cured at fluctuating low/freezing temperatures (+5 to −5 °C), representing the late fall and early spring seasons in northern regions. The mortar’s compressive strength increased with the incorporation of GBFS aggregate over the first three days of curing and decreased thereafter. A denser interfacial transition zone was captured around GBFS aggregates than NS in the three days old mortars. The deceleration influences of fluctuating low/freezing temperatures on the compressive strength development of mortars were diminished with time. Capillary water absorption increased with higher GBFS aggregate contents. Mortar with 25–50 vol.% GBFS aggregates exhibited greater frost resistance than control mortar with NS only. The incorporation of GBFS aggregate enhanced the mortar’s resistance against a sulfuric acid attack. This study demonstrates the potential of GBFS aggregate for use in construction under cold weather conditions

Additive manufacturing of geopolymer composites for sustainable construction: critical factors, advancements, challenges, and future directions

Increasing pollution poses enormous pressure on the global ecosystem, with a need to limit the carbon emissions from the construction materials industry. Mitigation of this carbon is possible by converting industrial wastes into alternative cement and optimisation in the building process. Taking this into account, advancement is taking place in sustainable geopolymer composites-based additive manufacturing (AM) technology. Typical precursors for geopolymer binder are industrial waste by-products (such as slag, fly ash, and metakaolin). In another aspect, AM entails several benefits such as easy fabrication, freedom of design, the ability to generate sophisticated structural elements and reduce: expenses, time, waste generation, and labor demands. This review journal paper on geopolymer AM presents a bibliometric study followed by an overview of AM methods and influencing parameters, techniques in geopolymer AM (such as extrusion and powder bed), materials, improvements in AM process, and fresh-state and hardened-state properties. Recent developments in AM processes within the geopolymer are critically discussed while investigating the properties and applications of the same. The discussion includes an analysis pinpointing research gaps essential in developing geopolymer AM

Strain hardening behavior of lightweight hybrid polyvinyl alcohol (PVA) fiber reinforced cement composites

Experimental results on the strain hardening and multiple cracking behaviors of polyvinyl alcohol (PVA) fiber reinforced cementitious composites under bending are reported in this paper. Different hybrid combinations of PVA fibers with different lengths and volume fractions are considered to reinforce the mortar matrix. Among different hybrid combinations, the composite containing 2% thicker PVA fibers of 12 mm length and 1% thinner PVA fibers of 6 mm length and the composite containing 2% thicker PVA fibers of 24 mm length and 1% thinner PVA fibers of 6 mm length showed the best performance in terms of highest ultimate load, largest CMOD (crack mouth opening displacement) at peak load and multiple cracking behavior. The effects of four types of light weight sands on the strain hardening and multiple cracking behavior of hybrid fiber composites are also evaluated in this study. It has been observed that the ultimate load and CMOD at peak load for all light weight hybrid fiber composites are almost the same irrespective of volume fractions of light weight sand. The composites containing finer light weight sands exhibited higher ultimate load than those containing coarser light weight sands. It is also observed that the hybrid fiber composite containing normal silica sand exhibited higher ultimate load than the composites with light weight sands

Global burden of 288 causes of death and life expectancy decomposition in 204 countries and territories and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

BACKGROUND Regular, detailed reporting on population health by underlying cause of death is fundamental for public health decision making. Cause-specific estimates of mortality and the subsequent effects on life expectancy worldwide are valuable metrics to gauge progress in reducing mortality rates. These estimates are particularly important following large-scale mortality spikes, such as the COVID-19 pandemic. When systematically analysed, mortality rates and life expectancy allow comparisons of the consequences of causes of death globally and over time, providing a nuanced understanding of the effect of these causes on global populations. METHODS The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 cause-of-death analysis estimated mortality and years of life lost (YLLs) from 288 causes of death by age-sex-location-year in 204 countries and territories and 811 subnational locations for each year from 1990 until 2021. The analysis used 56 604 data sources, including data from vital registration and verbal autopsy as well as surveys, censuses, surveillance systems, and cancer registries, among others. As with previous GBD rounds, cause-specific death rates for most causes were estimated using the Cause of Death Ensemble model-a modelling tool developed for GBD to assess the out-of-sample predictive validity of different statistical models and covariate permutations and combine those results to produce cause-specific mortality estimates-with alternative strategies adapted to model causes with insufficient data, substantial changes in reporting over the study period, or unusual epidemiology. YLLs were computed as the product of the number of deaths for each cause-age-sex-location-year and the standard life expectancy at each age. As part of the modelling process, uncertainty intervals (UIs) were generated using the 2·5th and 97·5th percentiles from a 1000-draw distribution for each metric. We decomposed life expectancy by cause of death, location, and year to show cause-specific effects on life expectancy from 1990 to 2021. We also used the coefficient of variation and the fraction of population affected by 90% of deaths to highlight concentrations of mortality. Findings are reported in counts and age-standardised rates. Methodological improvements for cause-of-death estimates in GBD 2021 include the expansion of under-5-years age group to include four new age groups, enhanced methods to account for stochastic variation of sparse data, and the inclusion of COVID-19 and other pandemic-related mortality-which includes excess mortality associated with the pandemic, excluding COVID-19, lower respiratory infections, measles, malaria, and pertussis. For this analysis, 199 new country-years of vital registration cause-of-death data, 5 country-years of surveillance data, 21 country-years of verbal autopsy data, and 94 country-years of other data types were added to those used in previous GBD rounds. FINDINGS The leading causes of age-standardised deaths globally were the same in 2019 as they were in 1990; in descending order, these were, ischaemic heart disease, stroke, chronic obstructive pulmonary disease, and lower respiratory infections. In 2021, however, COVID-19 replaced stroke as the second-leading age-standardised cause of death, with 94·0 deaths (95% UI 89·2-100·0) per 100 000 population. The COVID-19 pandemic shifted the rankings of the leading five causes, lowering stroke to the third-leading and chronic obstructive pulmonary disease to the fourth-leading position. In 2021, the highest age-standardised death rates from COVID-19 occurred in sub-Saharan Africa (271·0 deaths [250·1-290·7] per 100 000 population) and Latin America and the Caribbean (195·4 deaths [182·1-211·4] per 100 000 population). The lowest age-standardised death rates from COVID-19 were in the high-income super-region (48·1 deaths [47·4-48·8] per 100 000 population) and southeast Asia, east Asia, and Oceania (23·2 deaths [16·3-37·2] per 100 000 population). Globally, life expectancy steadily improved between 1990 and 2019 for 18 of the 22 investigated causes. Decomposition of global and regional life expectancy showed the positive effect that reductions in deaths from enteric infections, lower respiratory infections, stroke, and neonatal deaths, among others have contributed to improved survival over the study period. However, a net reduction of 1·6 years occurred in global life expectancy between 2019 and 2021, primarily due to increased death rates from COVID-19 and other pandemic-related mortality. Life expectancy was highly variable between super-regions over the study period, with southeast Asia, east Asia, and Oceania gaining 8·3 years (6·7-9·9) overall, while having the smallest reduction in life expectancy due to COVID-19 (0·4 years). The largest reduction in life expectancy due to COVID-19 occurred in Latin America and the Caribbean (3·6 years). Additionally, 53 of the 288 causes of death were highly concentrated in locations with less than 50% of the global population as of 2021, and these causes of death became progressively more concentrated since 1990, when only 44 causes showed this pattern. The concentration phenomenon is discussed heuristically with respect to enteric and lower respiratory infections, malaria, HIV/AIDS, neonatal disorders, tuberculosis, and measles. INTERPRETATION Long-standing gains in life expectancy and reductions in many of the leading causes of death have been disrupted by the COVID-19 pandemic, the adverse effects of which were spread unevenly among populations. Despite the pandemic, there has been continued progress in combatting several notable causes of death, leading to improved global life expectancy over the study period. Each of the seven GBD super-regions showed an overall improvement from 1990 and 2021, obscuring the negative effect in the years of the pandemic. Additionally, our findings regarding regional variation in causes of death driving increases in life expectancy hold clear policy utility. Analyses of shifting mortality trends reveal that several causes, once widespread globally, are now increasingly concentrated geographically. These changes in mortality concentration, alongside further investigation of changing risks, interventions, and relevant policy, present an important opportunity to deepen our understanding of mortality-reduction strategies. Examining patterns in mortality concentration might reveal areas where successful public health interventions have been implemented. Translating these successes to locations where certain causes of death remain entrenched can inform policies that work to improve life expectancy for people everywhere. FUNDING Bill & Melinda Gates Foundation

Mechanical and durability properties of fly ash geopolymer concrete containing recycled coarse aggregates

AbstractThis paper presents mechanical and durability properties of geopolymer concrete containing recycled coarse aggregate (RCA). The RCA is sourced from local construction and demolition (C&D) waste in Perth, Australia. The RCA is used as a partial replacement of natural coarse aggregate (NCA) in geopolymer concrete at 15%, 30% and 50% by wt. which corresponds to series two, three and four, respectively, while the geopolymer concrete containing 100% NCA is control and is considered as the first series. Class F fly ash is used as the source material for the geopolymer and 8M sodium hydroxide and sodium silicate alkali activators are used to synthesise the fly ash geopolymer in this study. In all four series a constant alkali activator to fly ash ratio is used. Compressive strength, indirect tensile strength and elastic modulus of above geopolymer concrete are measured at 7 and 28days, while sorptivity, immersed water absorption and volume of permeable voids of above geopolymer concrete are measured at 28days. Relevant Australian standards are used to measure all the above properties except the sorptivity which is measured according to ASTM standard. Results show that the compressive strength, indirect tensile strength and elastic modulus of geopolymer concrete decrease with an increase in RCA contents, which is also true for both 7 and 28days. Excellent correlations of compressive strength with indirect tensile strength and elastic modulus are also observed in geopolymer concrete containing RCA. Existing empirical models for cement concrete and geopolymer concrete containing NCA underestimate and overestimate the indirect tensile strength and elastic modulus, respectively of geopolymer concrete containing RCA. The measured durability properties such as sorptivity, water absorption and volume of permeable voids of geopolymer concrete were also adversely affected by the incorporation of RCA and these properties increase with an increase in RCA contents. The effects of RCA on the measured mechanical and durability properties of geopolymer concrete follow similar trend in cement concrete. Very good correlations of compressive strength with volume of permeable voids and water absorption of geopolymer concrete containing RCA are also observed, while the correlation between the compressive strength and the sorptivity is not that strong