Abstract

A smooth cold joint of concrete is an untreated weak plane caused by an interruption of the casting process, which can significantly affect the performance of a structural system. In this paper, the problem of the generation of cold joints is approached from two complementary perspectives. a) The loss of resistance due to the occurrence of cold joints is quantified through an extensive experimental program of concrete cylinders and b) a constitutive model is proposed and its performance is analyzed to simulate the time-dependent behavior of concrete under load (viscosity) and no load (setting). A loss of resistance over 30% for cold concrete cylinders with diagonal joints was found, while concrete cylinders with horizontal cold joints had no loss of resistance. Thus, the loss of resistance depends on the orientation of the cold joint with respect to the direction of the main stresses. This aspect is explained by the proposed constitutive model of viscous–reactive type, which is able to simulate the results of the experimental program. This work opens the possibility of numerical modeling of boundary value problems of structures with a cold joint and to study their influence on the structure’s overall stability.

Abstract

This paper presents a study of the behavior of reinforced concrete continuous deep beams by numerical simulation, where results of the numerical analysis are calibrated and validated from existing experimental results in the international literature. In the modeling, a bilinear model is considered with Von Mises failure criteria for reinforcing steel and Concrete Damage Plasticity for concrete, where a good correspondence was achieved between the numerical results to estimate the load capacity and the displacement between the reference numerical and experimental results. The adequate calibration of the physical-mechanical diagram of the experiment allows numerically studying the influence of different geometric factors and reinforcement configurations. The numerical study evidences the influence of the main and vertical reinforcements in the load capacity of these structures, where the most significant contribution of the vertical reinforcement is found in beams with higher shear spaneffective depth ratio (a/d). Diagrams of continuous deep beams with circular web openings are analyzed, showing favorable positions for the location of these openings and their direct influence on the load capacity reduction for beam diagrams with concentrated and distributed load.

Abstract

Steam curing is a process used to accelerate cement hydration reactions with the purpose of enhancing the mechanical strength of concrete at early ages, since hydration reactions are temperature dependent. To evaluate the influence of temperature on the development of mechanical properties of concrete the maturity concept was used. This method estimates the development of these properties according to the temperature history of concrete along the curing process. The temperature influence is indicated through the apparent activation energy (AE) value. The higher the AE value, the higher the energy amount will be necessary to start reactions, and thus the velocity of these reactions will be affected by temperature. This work is based on an experimental study of steam-cured concrete made with 5% and 10% of rice husk ash (RHA) addition in which the development of some mechanical properties was investigated. The rice husk ash used was obtained from uncontrolled combustion of rice husk, in an open chamber, without any temperature control or burning time. The mechanical property investigated was the compressive strength. Results indicate the influence of RHA addition and its dosage on the hydration reactions of cement and the mechanical properties of steam-cured concretes.

Abstract

This paper presents a comparative analysis of the deterioration of mortars containing 10% and 20% of a fluid catalytic cracking residue (FCC) in the presence of sodium sulfate (Na2SO4) and magnesium sulfate (MgSO4) at 5% (concentration 50g/L). Cement without addition (reference cement), and blended with 10% metakaolin (Cem-10MK) and 10% silica fume (Cem-10SF) were used as reference materials. The longitudinal expansion and loss of compressive strength at 392 days of exposure were evaluated. Additionally, microstructural analysis was performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) to identify the generated products. The results indicate that the residual strength of mortars blended with 10% and 20% of FCC after 360 days of immersion in the Na2SO4 solution is 18.5% higher than the value reported by the standard mixture, and 55% and 39% higher with respect to that reported for the mixtures containing 10% MK and SF. Mortars containing 10% of FCC in the presence of Na2SO4 report a loss of resistance of approximately 10%, while in MgSO4 it was 38% lower than the values of other evaluated mixtures. In general, MgSO4 is a more aggressive solution than Na2SO4. Ettringite and gypsum were identified as products from the reaction with sulfates.

Abstract

The lean ideal is to deliver customer value without waste. Traditional sustainability outcomes, which are attributed to the pursuit of the lean ideal in construction projects, consisted of economic outcomes instead of environmental outcomes. This paper explores how lean design methods can reduce construction and demolition (C&D) waste and contribute to environmental sustainability. Three case studies are conducted to analyze three hospital projects in California that employed lean tools and methods during design. These three cases demonstrate that C&D waste reduction (e.g., recycling construction waste, reducing material use, and enhancing recovery after use) can be indirectly achieved by economic waste reduction. Testable hypotheses were generated from the case study findings and were proposed as future research topics.

Abstract

In recent years, nanotechnology has emerged as an excellent tool for choosing materials for the architectural design of spaces that are sensitive to bacteria, such as hospitals, clinics, etc. This article deals with the main finishes. Graphene provides incomparable possibilities thanks to its properties. Its high bactericidal activity allows improving finishes.