Performance of High-volume Fly Ash Self-compacting Concrete Exposed to External Sulfate Attack

The high-volume fly ash concrete, HVFAC, could be defined as any concrete mix having fly ash content larger than 50 percent of the total cementitious materials content. Due to the availability of fly ash in large quantities globally with low cost, HVFAC could be considered as a solution for the environmental impact of Portland cements. In this study the durability of two high-volume fly ash self-compacting concrete, HVFASCC, mixes exposed to the effects of two sulfate aggressive solutions was investigated. The fly ash, class F, contents for these mixes were 50 and 60 percent by weight of Portland cement. The external sulfate attack was simulated by submerging the concrete specimens in 5 percent sodium and magnesium sulfate solutions separately for 240 days. Six mixes were produced for this purpose, they were: 2 reference mixes cured in water, 2 mixes submerged in Na2SO4 solution and 2 mixes submerged in MgSO4 solution. The testing program includes: slump flow, V-funnel, L-box, weight change, XRD and the strength tests: compressive, splitting and flexural strengths. The fly ash content has a positive effect on the rheology (workability) of all tested mixtures. In other words, increasing the cement replacement level from 50 to 60 percent has enhanced the filling ability, passing ability, and segregation resistance of the investigated SCC mixes. The test results show that the magnesium solution has the higher harmful effect on all mixes than the sodium solution. The replacements of Portland cement by the assigned percentages of fly ash have significantly increased the resistance of SCC to the external sulfate attack due to lime consuming reaction

A Statistical Model to Predict the Strength Development of Geopolymer Concrete Based on SiO2/Al2O3 Ratio Variation

Geopolymer Concrete (GPC) is a new class of concrete that presents a vital improvement in sustainability and the environment, particularly in recycling and alternative construction methods. Geopolymers offer a sustainable, low energy consumption, low carbon footprint, and a 100% substitute for the Portland cement binder for civil infrastructure applications. Furthermore, many aluminosilicate materials can be obtained as by-products of other processes, such as coal combustion or the thermal pulping of wood. In addition, slag and fly ash are necessary to source materials for geopolymer. Therefore, geopolymer is considered a solution for waste management that can minimize greenhouse gas emissions. In this statistical study, the present experimental work and found experimental data were collected from local and international literature and were used to build and validate the statistical models to predict the strength development of Geopolymer concrete with binary and ternary systems of source materials. The main independent variable was R, representing the ratio of SiO2/Al2O3by weight in the source material. The investigated range of R was 1.42–3.6. Nine concrete geopolymer mixes with R in the above range represent the experimental part carried out. The targeted properties were compressive, splitting, and flexural strengths. The experimental results showed that the R ratio significantly influences the mechanical performance of the final product. The compressive strength improved by 82, 86, 93, and 95%, when metakaolin content was partially replaced by fly ash and GGBS by percentages of 30, 70, 72, 90, and 95% for mixes 2, 3, 5, 7, and 8 respectively. Also, when GGBS partially replaced fly ash content by 36% and 100% for mixes 6 and 9, compressive strength improved by 10.6% and 41.8%, respectively, compared to mix4. Furthermore, the statistical study revealed that the R ratio might be utilized to determine geopolymer strength with reasonable accuracy. The built models were developed by linear and non-linear regression analysis using SPSS software, version 25. Doi: 10.28991/CEJ-2022-08-03-04 Full Text: PD

Mortality from gastrointestinal congenital anomalies at 264 hospitals in 74 low-income, middle-income, and high-income countries: a multicentre, international, prospective cohort study

Summary Background Congenital anomalies are the fifth leading cause of mortality in children younger than 5 years globally. Many gastrointestinal congenital anomalies are fatal without timely access to neonatal surgical care, but few studies have been done on these conditions in low-income and middle-income countries (LMICs). We compared outcomes of the seven most common gastrointestinal congenital anomalies in low-income, middle-income, and high-income countries globally, and identified factors associated with mortality. Methods We did a multicentre, international prospective cohort study of patients younger than 16 years, presenting to hospital for the first time with oesophageal atresia, congenital diaphragmatic hernia, intestinal atresia, gastroschisis, exomphalos, anorectal malformation, and Hirschsprung’s disease. Recruitment was of consecutive patients for a minimum of 1 month between October, 2018, and April, 2019. We collected data on patient demographics, clinical status, interventions, and outcomes using the REDCap platform. Patients were followed up for 30 days after primary intervention, or 30 days after admission if they did not receive an intervention. The primary outcome was all-cause, in-hospital mortality for all conditions combined and each condition individually, stratified by country income status. We did a complete case analysis. Findings We included 3849 patients with 3975 study conditions (560 with oesophageal atresia, 448 with congenital diaphragmatic hernia, 681 with intestinal atresia, 453 with gastroschisis, 325 with exomphalos, 991 with anorectal malformation, and 517 with Hirschsprung’s disease) from 264 hospitals (89 in high-income countries, 166 in middleincome countries, and nine in low-income countries) in 74 countries. Of the 3849 patients, 2231 (58·0%) were male. Median gestational age at birth was 38 weeks (IQR 36–39) and median bodyweight at presentation was 2·8 kg (2·3–3·3). Mortality among all patients was 37 (39·8%) of 93 in low-income countries, 583 (20·4%) of 2860 in middle-income countries, and 50 (5·6%) of 896 in high-income countries (p<0·0001 between all country income groups). Gastroschisis had the greatest difference in mortality between country income strata (nine [90·0%] of ten in lowincome countries, 97 [31·9%] of 304 in middle-income countries, and two [1·4%] of 139 in high-income countries; p≤0·0001 between all country income groups). Factors significantly associated with higher mortality for all patients combined included country income status (low-income vs high-income countries, risk ratio 2·78 [95% CI 1·88–4·11], p<0·0001; middle-income vs high-income countries, 2·11 [1·59–2·79], p<0·0001), sepsis at presentation (1·20 [1·04–1·40], p=0·016), higher American Society of Anesthesiologists (ASA) score at primary intervention (ASA 4–5 vs ASA 1–2, 1·82 [1·40–2·35], p<0·0001; ASA 3 vs ASA 1–2, 1·58, [1·30–1·92], p<0·0001]), surgical safety checklist not used (1·39 [1·02–1·90], p=0·035), and ventilation or parenteral nutrition unavailable when needed (ventilation 1·96, [1·41–2·71], p=0·0001; parenteral nutrition 1·35, [1·05–1·74], p=0·018). Administration of parenteral nutrition (0·61, [0·47–0·79], p=0·0002) and use of a peripherally inserted central catheter (0·65 [0·50–0·86], p=0·0024) or percutaneous central line (0·69 [0·48–1·00], p=0·049) were associated with lower mortality. Interpretation Unacceptable differences in mortality exist for gastrointestinal congenital anomalies between lowincome, middle-income, and high-income countries. Improving access to quality neonatal surgical care in LMICs will be vital to achieve Sustainable Development Goal 3.2 of ending preventable deaths in neonates and children younger than 5 years by 2030

FFECT OF POZOOLANIC MATERIALS ON COMPRESSIVE STRENGTH OF GEOPOLYMER CONCRETE

The development that has occurred in industries and technologies after the Industrial Renaissance and beyond has led to consume a large amount of raw materials. The huge consumption of these materials is hard to be compensated. Therefore, it is necessary to find materials that can be recycled and environmentally friendly materials. Hence, the idea of sustainability, which states, the ability to meet our current needs without compromising the ability of future generation to meet theirs. It has become an urgent to produce materials that called environmentally friendly or sustainable materials. In the field of civil engineering, an important role has been played in producing of environmentally friendly concrete by using pozollanic materials. Using environmentally friendly concrete instead of traditional concrete can participate in reducing the effect of global warming. In this research, local materials like metakaolin and pozollanic materials such as, fly ash and grand granulated blast furnace slag GGBFS were used in the production of an environmentally friendly concrete which they are called Geopolymer concrete. The effect of pozzolanic material type and mixing ratios on compressive strength at 7, 28 and 60 days were studied