Influence of dry and wet curing conditions on compressive strength of silica fume concrete

This paper reports a part of an ongoing laboratory investigation in which the compressive strength of silica fume concrete is studied under dry and wet curing conditions. In the study, a total of 48 concretes, including control Portland cement concrete and silica fume concrete, were produced with four different water-cement ratios (0.3, 0.4, 0.5, 0.6), three different cement dosages (350, 400, 450 kg/m3) and three partial silica fume replacement ratios (10%, 15%, 20%). A hyperplastisizer was used in concrete at various quantities to provide and keep a constant workability. Three cubic samples produced from fresh concrete were demoulded after a day; then, they were cured at 20±2 °C with 65% relative humidity (RH), and three other cubic samples were cured at 20±2 °C with 100% RH until the samples were used for compressive strength measurement at 28 days. The comparison was made on the basis of compressive strength between silica fume concrete and control Portland cement concrete. Silica fume concretes were also compared among themselves. The comparisons showed that compressive strength of silica fume concrete cured at 65% RH was influenced more than that of Portland cement concrete. It was found that the compressive strength of silica fume concrete cured at 65% RH was, at average, 13% lower than that of silica fume concrete cured at 100% RH. The increase in the water-cementitious material ratios makes the concrete more sensitive to dry curing conditions. The influence of dry curing conditions on silica fume concrete was marked as the replacement ratio of silica fume increased. © 2005 Elsevier Ltd. All rights reserved

The influence of aggregate type on the strength and abrasion resistance of high strength concrete

This paper examines the influence of aggregate type on the strength characteristics and abrasion resistance of high strength silica fume concrete. Five different aggregate types (gabbro, basalt, quartsite, limestone and sandstone) were used to produce high strength concrete containing silica fume. Silica fume replacement ratio with cement was 15% on a mass basis. Water-binder ratio was 0.35. The amount of hyperplasticizer was 4% of the binder content by mass. Gabbro concrete showed the highest compressive and flexural tensile strength and abrasion resistance, while sandstone showed the lowest compressive and flexural tensile strength and abrasion resistance. High abrasion resistant aggregate produced a concrete with high abrasion resistance. Three-month compressive strengths of concretes made with basalt, limestone and sandstone were found to be equivalent to the uniaxial compressive strengths of their aggregate rocks. However, the concretes made with quartsite and gabbro aggregate showed lower compressive strength than the uniaxial compressive strength of their aggregate rocks. © 2007 Elsevier Ltd. All rights reserved

Strength properties of roller compacted concrete containing a non-standard high calcium fly ash

Although roller compacted concrete (RCC) made with and without fly ash (FA) has enjoyed numerous application of dams, roads and large floors construction in Europe, Japan, Australia and Unites States since 1970s, it has not almost yet been used at all in Turkey despite abundant and economical sources of FA and cement. This reluctance has arised due to the lack of confidence and the lack of technical experience in the concrete engineering field. In order to build, to some extend, the confidence and gain technical experience about RCC made with and without FA, a series of laboratory work was undertaken. In the present work, the RCCs were produced with three different cement quantity including 200, 300 and 400 kg/m3 normal Portland cement (NPC). A FA, which is a local material, was also used in the concrete production with the replacement level of 0%, 15%, 30% and 45% by mass of NPC. The FA used was a non-standard and high calcium fly ash. Water-cementitious material ratios were determined using the vibrating slump test. Concrete cube, prism and cylinder specimens were prepared by vibration until complete compaction obtained. The compressive, flexural tensile and splitting tensile tests were carried out. Although the FA used was non-standard, the test results showed that it can replace the cement between 15% and 30% by mass, because FA concrete attained comparable or higher strength properties to the corresponding NPC concrete. From the strength properties of view, it was concluded that RCCs produced and tested could be an alternative material for road paving or large floors construction. © 2003 Elsevier B.V. All rights reserved.Firat University Scientific Research Projects Management Unit: FBE2002D179Authors thank to Çukurova University Scientific Research Project for financial support to this work (project number: FBE2002D179)

The influence of aggregate type on the strength and abrasion resistance of high strength concrete

WOS: 000255086900005This paper examines the influence of aggregate type on the strength characteristics and abrasion resistance of high strength silica fume concrete. Five different aggregate types (gabbro, basalt, quartsite, limestone and sandstone) were used to produce high strength concrete containing silica fume. Silica fume replacement ratio with cement was 15% on a mass basis. Water-binder ratio was 0.35. The amount of hyperplasticizer was 4% of the binder content by mass. Gabbro concrete showed the highest compressive and flexural tensile strength and abrasion resistance, while sandstone showed the lowest compressive and flexural tensile strength and abrasion resistance. High abrasion resistant aggregate produced a concrete with high abrasion resistance. Three-month compressive strengths of concretes made with basalt, limestone and sandstone were found to be equivalent to the uniaxial compressive strengths of their aggregate rocks. However, the concretes made with quartsite and gabbro aggregate showed lower compressive strength than the uniaxial compressive strength of their aggregate rocks. (c) 2007 Elsevier Ltd. All rights reserved

High-mobility group box 1 restores cardiac function after myocardial infarction in transgenic mice

Aim: High-mobility group box 1 (HMGB1) is a nuclear DNA-binding protein and is released from necrotic cells, inducing inflammatory responses and promoting tissue repair and angiogenesis. To test the hypothesis that HMGB1 enhances angiogenesis and restores cardiac function after myocardial infarction, we generated transgenic mice with cardiac specific overexpression of HMGB1 (HMGB1-Tg) using α-myosin heavy chain (MHC) promoter. Methods and Results: The left anterior descending coronary artery was ligated in HMGB1-Tg and wild-type littermate (Wt) mice. After coronary artery ligation, HMGB1 was released into circulation from the necrotic cardiomyocytes of HMGB1 overexpressing hearts. The size of myocardial infarction was smaller in HMGB1-Tg than in Wt mice. Echocardiography and cardiac catheterization demonstrated that cardiac remodeling and dysfunction after myocardial infarction were prevented in HMGB1-Tg mice compared to Wt mice. Furthermore, survival rate after myocardial infarction of HMGB1-Tg mice was higher than that of Wt mice. Immunohistochemical staining revealed that capillary and arteriole formations after myocardial infarction were enhanced in HMGB1-Tg mice. Conclusions: We demonstrated the first in vivo evidence that HMGB1 enhances angiogenesis, restores cardiac function, and improves survival after myocardial infarction. These results may provide a novel therapeutic approach for left ventricular dysfunction after myocardial infarction

The von Hippel–Lindau tumor suppressor gene product represses oncogenic β-catenin signaling in renal carcinoma cells

Loss of von Hippel–Lindau (VHL) tumor suppressor gene function occurs in familial and most sporadic clear cell renal cell carcinoma (RCC), resulting in the aberrant expression of genes that control cell proliferation, invasion, and angiogenesis. The molecular mechanisms by which VHL loss leads to tumorigenesis are not yet fully defined. VHL loss has been shown to allow robust RCC cell motility, invasiveness, and morphogenesis in response to hepatocyte growth factor (HGF) stimulation, processes that are known to contribute to tumor invasiveness and metastatic potential. Among the most likely intracellular mediators of these HGF-driven activities is β-catenin, a structural link between cadherens and the actin cytoskeleton, as well as a gene transactivator. We show that reconstitution of VHL expression in RCC cells repressed HGF-stimulated β-catenin tyrosyl phosphorylation, adherens junction disruption, cytoplasmic β-catenin accumulation, and reporter gene transactivation in RCC cells. Ectopic expression of a ubiquitination-resistant β-catenin mutant specifically restored HGF-stimulated invasion and morphogenesis in VHL-transfected RCC cells. VHL gene silencing in non-RCC renal epithelial cells phenotypically mimicked VHL loss in RCC, and HGF-driven invasiveness was blocked by the expression of a dominant-negative mutant of Tcf. We conclude that, unlike many other cancers, where HGF pathway activation contributes to malignancy through the acquisition of autocrine signaling, receptor overexpression, or mutation, in RCC cells VHL loss enables HGF-driven oncogenic β-catenin signaling. These findings identify β-catenin as a potential target in biomarker and drug development for RCC