Sustainable Concrete for the 21st Century Concept of Strength through Durability

The world is passing through difficult and troubled times, and we live in a rapidly changing world. The construction industry is facing many challenges – global warming, climate change forces, and the capability to achieve sustainable development and economic progress without damaging our environment. The concrete industry in particular faces further challenges. There is extensive evidence to show that concrete materials and concrete structures all over the world are deteriorating at a rapid rate, and that we are unable to ensure their long-term durable service life performance. To confound this situation, we are also faced with an urgent need to regenerate our infrastructure systems if we are to eradicate poverty and provide a decent Quality of Life for all the peoples of the world. This paper shows that the current emphasis on high strength and very high strength, and the design philosophy of Durability through Strength for concrete materials and concrete structures is fundamentally flawed. It is this misleading concept and vision that is primarily responsible for the lack of durable performance of concrete in real life environments. To change this scenario, this paper advocates that concrete materials must be manufactured for durability and not for strength. It is shown that this concept of Strength through Durability can be achieved through careful design of the cement matrix and its microstructure. If concrete is to be an eco-friendly, and sustainable driving force and construction material for social change, the need is to produce durable concrete with strengths of 30 to 60 to 80 MPa rather than very high strength concrete without an assured durable performance

A design model for punching shear of FRP-reinforced slab-column connections

The overall aim of this paper is to develop a unified design method for the punching shear resistance of slab-column connections irrespective of the type of internal reinforcement. In the first part of the paper a design model for the punching shear resistance of concrete slab-column connections reinforced with fibre-reinforced polymers (FRP) is proposed. This design model is based on the authors’ theoretical analysis for such slabs, which considers the physical behavior of the connections under load. The effects of the inherent linear brittle response, the lower elastic modulus and the different bond features, as compared to steel, of the FRP reinforcement are all accounted for in the present study. The proposed model does not incorporate any fitting factors to match the theory to the trend of the available FRP slab test results. The excellent agreement between the predicted and published test results should give confidence to engineers and designers in using FRP as a sound structural reinforcement for slab-column connections. It is then shown that the proposed design model for FRP slabs and the previous model of the authors for steel reinforced slabs are both identical in nature and structure, thus constituting a unified approach to design for punching shear in slabs. On the basis of the unified model comparison and correlation between an FRP slab and a reference steel reinforced slab, confirmed by the available test results, are presented. The unified model also enables the development of a more rational and reliable equivalent steel reinforcement ratio which can be applied to existing code equations for steel reinforced slabs to estimate the punching resistance of FRP-reinforced slabs

Calculation of ground states of four-dimensional +or- J Ising spin glasses

Ground states of four-dimensional (d=4) EA Ising spin glasses are calculated for sizes up to 7x7x7x7 using a combination of a genetic algorithm and cluster-exact approximation. The ground-state energy of the infinite system is extrapolated as e_0=-2.095(1). The ground-state stiffness (or domain wall) energy D is calculated. A D~L^{\Theta} behavior with \Theta=0.65(4) is found which confirms that the d=4 model has an equilibrium spin-glass-paramagnet transition for non-zero T_c.Comment: 5 pages, 3 figures, 31 references, revtex; update of reference

Thaumasite form of sulfate attack in limestone cement mortars: A study on long term efficiency of mineral admixtures

Concrete and mortar made from limestone cement may exhibit a lack of durability due to the formation of thaumasite. The addition of minerals that improve the concrete durability is expected to slow down the formation of thaumasite. in this work the effect of natural pozzolana, fly ash, ground granulated blast-furnace slag and metakaolin on the thaumasite formation in limestone cement mortar is examined. A limestone cement, containing 15% w/w limestone, was used. Mortar specimens were prepared by replacing a part of limestone cement with the above minerals. The specimens were immersed in a 1.8% MgSO4 solution and cured at 5 and 25 degrees C. The status of the samples after a storage period of 5 years was reported based on visual inspection, compressive strength, mass measurements, ultrasonic pulse velocity measurements and analytical techniques. It is concluded that the use of specific minerals, as partial replacement of cement, inhibits thaumasite formation in limestone cement mortar. (C) 2008 Elsevier Ltd. All rights reserved

SARS-CoV-2 infects the human kidney and drives fibrosis in kidney organoids

Kidney failure is frequently observed during and after COVID-19, but it remains elusive whether this is a direct effect of the virus. Here, we report that SARS-CoV-2 directly infects kidney cells and is associated with increased tubule-interstitial kidney fibrosis in patient autopsy samples. To study direct effects of the virus on the kidney independent of systemic effects of COVID-19, we infected human-induced pluripotent stem-cell-derived kidney organoids with SARS-CoV-2. Single-cell RNA sequencing indicated injury and dedifferentiation of infected cells with activation of profibrotic signaling pathways. Importantly, SARS-CoV-2 infection also led to increased collagen 1 protein expression in organoids. A SARS-CoV-2 protease inhibitor was able to ameliorate the infection of kidney cells by SARS-CoV-2. Our results suggest that SARS-CoV-2 can directly infect kidney cells and induce cell injury with subsequent fibrosis. These data could explain both acute kidney injury in COVID-19 patients and the development of chronic kidney disease in long COVID

High performance cement based materials and holistic design for sustainability in construction (Part I)

The cement/concrete industry is faced with two major challenges – an infrastructure crisis, and a sustainability problem. Both are worldwide issues with tremendous implications not only for ourselves but also for the lives of generations to come. The focus of this paper is to show that a holistic approach to the formulation and fabrication of concrete materials with emphasis on durability, ductility, environment and sustainability can lead to the development of a large number of eco-friendly and innovative cement-based construction materials for a wide range of applications in infrastructure regeneration and reconstruction. Quality of life is the one single goal that all humanity wants and aspires for, and a judicious combination of pozzolanic/cementitious materials, chemical admixtures, fillers, fibres and other appropriate constituents can meet the insatiable demand for basic infrastructure facilities and at the same time contribute to sustainable growth with the least damage to our environment. The paper illustrates this philosophy of manufacturing and designing sustainable concrete materials for durability rather than for strength with various examples such as fly ash/slag concrete, high volume fly ash concrete, structural lightweight aggregate concrete, low energy-cements, and fibre reinforcement. It is also shown that the philosophy of holistic design with emphasis on material stability, structural integrity and ductility can successfully meet the challenges of the infrastructure crisis and sustainable development of the concrete industry