Size And High Temperature Effects On The Compressive Strength Of Self Compacting Concretes

The compressive strength behavior of concrete is one of the fundamental parameters of structural design as most load-bearing concrete elements, such as beams, columns and slabs. However, it was known that compressive behavior of the concrete elements alter depend on the element size and exposed temperature conditions. When the slenderness (height/diameter) of the concrete elements increased, compressive strength decreased relatively and this behavior known as size effect. In this study, compressive strength variation of the self compacting concrete specimens investigated taking in to account the different slenderness ratio and exposure temperatures. For this purpose, a self compacting mixture was prepared with water to cement ratio of 0.40 and 450 kg/m3 cement dosage. Cylindrical specimens with the diameter of 100 mm and slenderness of 2.0, 1.5, 1.0, and 0.5 were prepared and exposed to the different high temperatures (400, 600 and 800 oC) for an hour. For a control purpose, same size specimens were also tested under the laboratory conditions. The results show that high temperature exposure has severe strength loss effect on the concrete specimens irrespective of the slenderness ratio. Increasing the exposure temperature increased the strength loss of the specimens drastically. Moreover, it was seen that relative strength change (decrease) is evident when specimens' size increased

Behaviour of Geopolymer Mortars after Exposure to Elevated Temperatures

In this study it was investigated the behavior of class F fly ash based geopolymer mortars subjected to elevated temperatures. Geopolimer composites were prepared with CEN-sand, water, fly ash as the binder, nSiO2Na2O and NaOH mixture combination as alkali activator. After mixing fresh geopolymer mixture, prismatic specimens were prepared using 40 mm × 40 mm × 160 mm prism molds. After molding, fresh geopolymer mortar samples with their mold were subjected to heat curing at 50 °C, 60 °C, 70 °C, 80 °C, 90 °C and 100 °C temperature for 48 hours in an oven. After 48 hours initial heat curing, the hardened samples were taken out of their mold. Then, they were further cured by leaving them in laboratory environment at about 22 ± 2 °C temperature, until 28 days together with heat curing duration. At the end of 28 days, geopolymer mortar samples developed flexural strength values between 2,9 MPa and 8,51 MPa. Geopolymer mortar samples developed compressive strength values between 7,63 MPa and 50,64 MPa. High temperature experiments were conducted to observe behaviour of geopolymer mortars at elevated temperatures. The control cement mortar mixtures were also prepared and subjected to high temperature exposure in comparison to geopolymer mortar mixtures. Control cement mortars were cured at laboratory environment for 28 days without initial temperature curing. Control cement mortar mixtures and geopolymer mortar mixtures were exposed to elevated temperatures of 200 °C, 400 °C, 600 °C and 800 °C temperature. The unit weight, ultrasonic pulse velocity, flexural and compressive strength of all mixtures were measured before and after high temperature exposure. Scanning electron microscope (SEM) images of the mixtures were taken and X-ray fluorescence (XRF) spectrometer analyses were carried out. It was observed that there was an increase in the flexural and compressive strengths of some geopolymer mortars after high temperature exposure. In general, geopolymer mortars exhibited better performance at elevated temperatures in comparison to control cement mortar mixture. DOI: http://dx.doi.org/10.5755/j01.ms.24.4.18829</p

Comparison of multi layer perceptron (MLP) and radial basis function (RBF) for construction cost estimation: the case of Turkey

In Turkey, for the preliminary construction cost estimation, a notice, which is updated and published annu­ally by Turkish Ministry of the Environment and Urbanism, known as “unit area cost method” (UACM) is generally employed. However, it’s known that the costs obtained through this method in which only construction area is taken into consideration have significant differences from actual costs. The aim of this study is to compare the cost estimations obtained through “multi layer perceptron” (MLP) and “radial basis function” (RBF), which are commonly used artificial neural network (ANN) methods. The results of MLP and RBF were also compared with the results of UACM and the validity of UACM was interpreted. Dataobtained from 232 public construction projects, which completed between 2003 and 2011 in different regions of Turkey, were reviewed. Consequently, estimated costs obtained from RBF were found to be higher than the actual costs with a 0.28% variance, while the estimated costs obtained from MLP were higher than actual values with a 1.11% variance. The approximate costs obtained from UACM are higher than actual costs with a 28.73% variance. It was found that both ANN methods were showed better performance than the UACM but RBF was superior to MLP. First published online: 24 Aug 201

Strength properties of slag/fly ash blends activated with sodium metasilicate

U radu se analizira alkalno aktiviranje mješavina morta koje sadrže mljevenu granuliranu zguru iz visokih peći i leteći pepeo, pri čemu se aktivacija odvija pomoću natrijevog metasilikata. Analiziraju se dvije serije te je izmjerena tlačna čvrstoća. Rezultati dobiveni za prvu seriju pokazuju da se tlačna čvrstoća bitno smanjuje sa smanjenjem omjera zgure i letećeg pepela. Trodnevna tlačna čvrstoća morta njegovanog pri temperaturi 100 °C donekle se povećava do omjera 60/40, ali se bitno smanjuje pri omjeru 40/60.The alkali activation of mortar blends containing Ground Granulated Blast Furnace Slag and Fly Ash, with activation based on sodium metasilicate, is investigated in this study. Two series are investigated, and compressive strength is measured. The results of the first series show that the compressive strength decreases considerably with a decrease in the slag and fly ash ratio. The 3-day compressive strength of mortar cured at the temperature of 100°C increases slightly up to the ratio of 60/40, but decreases considerably at the 40/60 ratio

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Abrasion-porosity-strength model for fly ash concrete

The durability of a concrete road to abrasive forces can be assessed effectively by measuring its abrasion resistance. This technical note reports the findings of a laboratory study including compressive strength, abrasion, and porosity properties of concrete mixtures made with fly ash and normal portland cement. The study involves two replacement ratios of fly ash, various water-cement ratios, the use of a superplasticizer, two curing conditions, and four concrete ages. Statistical models that relate abrasion to strength and porosity are presented

High volume fly ash abrasion resistant concrete

In this work, the abrasion resistance of high volume fly ash concrete was investigated. Concrete mixtures containing a large amount of fly ash replacing the cement in mass basis at 50 and 70% were prepared with various water-cementitious material ratios. A specially selected superplasticizer was employed to maintain the workability of the concrete. Volume loss of the specimen was considered as the abrasion value measured using a Dorry abrasion machine. Comparisons were made between normal portland cement (NPC) concrete and fly ash concrete. Comparisons were also made between fly ash concretes with 50 and 70% replacement. Investigation results have shown that the abrasion resistance increased as compressive strength increased. Analysis of the results showed that, for high strength grades (>40 MPa), the abrasion resistance of high volume fly ash concrete with 70% replacement with cement was found to be higher than that of counterpart control NPC concrete and concrete made with 50% fly ash. Superplasticizer and curing conditions have no significant influence on the general trend of the abrasion of concrete studied

Carbonation-porosity-strength model for fly ash concrete

The potential of a concrete for carbonation can be assessed effectively by measuring its carbonation depth using an accelerated carbonation testing. This paper reports the findings of a laboratory study including compressive strength, accelerated carbonation depth, and porosity properties of concrete mixtures made with fly ash and normal portland cement. The study involves two replacement ratios of fly ash, various water-to-cement ratios, use of superplasticizer, two curing conditions, and four concrete ages. Statistical models that relate accelerated carbonation depth to strength and porosity are presented