Numerical Study of Concrete

Concrete is one of the most widely used construction material in the word today. The research in concrete follows the environment impact, economy, population and advanced technology. This special issue presents the recent numerical study for research in concrete. The research topic includes the finite element analysis, digital concrete, reinforcement technique without rebars and 3D printing

Mechanical, structural and microstructural investigations of a novel concrete for special structural applications

Degradation of concrete members exposed to sulphuric acid environments is a key durability issue that affects the life cycle performance and maintenance costs of civil infrastructures. Groundwater, chemical waste, sulphur bearing compounds in backfill, acid rain in industrial zones and biogenic acid in sewage systems are the main sources of sulphuric acid affecting concrete structures. In this research, as part of an ongoing research on development of novel concretes for special applications, an acid resistant mortar (ARM) with current applications in lining and repair purposes was converted to acid resistant concrete in the laboratory and investigated for structural applications in acidic environments. Mechanical properties of the initial acid resistant mortar material, this novel acid resistant concrete (ARC) and a type of conventional concrete (CC), as the control, have been studied in the laboratory subjected to an accelerated test, 7% (by volume) sulphuric acid. The studied mechanical properties included compressive strength, modulus of elasticity (MOE), modulus of rupture (MOR) and indirect tensile strength tests. Apart from acid resistance experiments, other important properties for a structural concrete such as drying shrinkage and concrete performance subjected to high rate strain loads and elevated temperatures were also evaluated for ARC and CC. Structural performance of reinforced concrete (RC) flexural members made of this new concrete (ARC) and CC was assessed before and after different periods of continuous immersion in 7% sulphuric acid solution through static and cyclic loading under four-point bending tests to detect the effects of acid attack on structural performance of RC beams. Load- deflection behaviour, curvature- moment resistance at mid span, ultimate load capacity, ductility factor, stiffness degradation, dissipated energy and damping ratio were the main variables studied in these experiments. Application of ARC in beam-column joints, as another application for this concrete was also investigated due to possessing higher ductility than conventional concrete in mechanical properties tests aiming at reduction of transverse reinforcing bars in such members and the potential for seismic applications. Structural elements (i.e., beams and joints) were also modelled by using FE software ATENA to analyse the experimental results numerically. Microstructural characterisation was also performed on ARC and CC samples before and after acid exposure using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray mapping (XRM) and X-ray diffraction (XRD) to gain a better understanding regarding the change of microstructure of materials after exposure to acid. ARC showed superior performance than CC after exposure to acid in terms of loss of mechanical properties. Structural performance of ARC has been comparable to CC before exposure to acid and after a long period of exposure to acid it showed better performance than CC, particularly in terms of load bearing capacity. The application of ARC in beam-column joints allowed reducing transverse reinforcing bars in these joints (50% compared to CC). Microstructural characterisation also revealed significant facts regarding the deterioration mechanism in both types of concretes and their effect on mechanical properties

Physical Sulphate Attack on Concrete

Field experience with concrete exposed to sulphates has often shown that concrete can suffer from surface scaling above the ground level caused by physical sulphate attack. This type of attack has been ignored and, in some instances, confused with chemical sulphate attack. In addition, current standards that evaluate the performance of concrete under sulphate attack, only deal with the chemical aspects of sulphate attack. This lack of information has led to confusion and contradictory views regarding the mechanisms of concrete deterioration due to physical sulphate attack. In the current thesis, the performance of concrete exposed to environments prone to physical sulphate attack was investigated. The effects of mineral additives, water-to binder (w/b) ratio, along with various curing conditions on the performance of concrete exposed to physical sulphate attack was studied. In addition, the effectiveness of different surface treatment materials in mitigating physical sulphate attack on concrete was explored. Results show that concrete can experience dual sulphate attack. The lower immersed portion can suffer from chemical sulphate attack, while the upper portion can be vulnerable to physical attack. Lowering the w/b ratio and moist-curing the concrete reduced surface scaling above the solution level since the volume of pores was decreased. Although partial replacement of cement with pozzolans also decreased the pore volume, surface scaling increased due to the increased proportion of small diameter pores and the associated growth of capillary suction and surface area for evaporation. Epoxy- and silane-based surface treatment materials were found to be adequate for protecting both cured and non-cured concrete exposed to physical sulphate attack. However, it was found that adequate curing of the concrete before coating is important to eliminate the separation of the surface treatment based on bitumen and to enhance the resistance of concrete to physical sulphate attack. Using a water-based solid acrylic polymer resin did not provide adequate protection of concrete against physical sulphate attack

Expansive mineral growth and concrete deterioration: a microstructural and microanalytical study

In order to evaluate the role of newly-formed minerals in premature deterioration of highway concrete, a three-phase study was undertaken. In the first phase, petrographic and SEM/EDAX analyses were performed to determine chemical and mineralogical changes in the aggregate and cement paste of samples taken from Iowa highways that showed premature deterioration. In the second phase, experimental simulations of environmental changes in highway concrete after applying different deicer chemicals were conducted to evaluate the role of deicers in premature deterioration. In the third phase, experiments were done to evaluate whether crystallization inhibitors can reduce damage and the growth of secondary minerals in concrete and to help understand the mechanism of deterioration by secondary mineral growth in concrete;In the first phase of study, it was evidenced that two major expansive minerals, ettringite and brucite, were responsible for premature deterioration. Severe expansion cracking of cement paste was often associated with ettringite locations, and strongly suggests that secondary ettringite was a major cause. Brucite forms in cement paste of concretes containing reactive dolomite aggregate via dedolomitization reactions. No cracking was observed to be spatially associated with brucite, but expansion stresses associated with its growth at innumerable microlocations might be relieved by cracking at weaker locations in the concrete;Deicer salts cause characteristic concrete deterioration by altering dedolomitization rims at the coarse-aggregate paste interface, altering cement paste and/or forming new secondary minerals. Magnesium in deicer solutions caused the most severe paste deterioration by forming non-cementitious magnesium silicate hydrate and brucite. Chloride in deicer solutions promotes decalcification of paste. CMA and Mg-acetate produced the most deleterious effects on concrete, with Ca-acetate being much less aggressive. In order to use CMA as an alternative deicer and to prevent premature deterioration, it is recommended that it possess a high Ca/Mg ratio;Three types of commercially inhibitor chemicals, polyphosphonate, polyacrylate, and phosphate ester, were effective in reducing the formation of ettringite and also in reducing concrete expansion due to ettringite. Phosphonate inhibitors are the most effective among those inhibitors. These inhibitors are not effective in preventing formation of brucite and MSH from CMA and magnesium acetate solution

Advances in the understanding of the role of degree of saturation and water distribution in mechanical behaviour of calcarenites using magnetic resonance imaging technique

A thorough knowledge of the variations of mechanical properties of rock materials with their water content is essential for evaluating the structural behaviour and durability of stone constructions exposed to different moist environments during their lifetime and for solving a broad range of rock mechanics issues. In this study, the effect of degree of saturation (Sr) and water distribution inside pore network on mechanical parameters such as Uniaxial Compressive Strength, Young’s modulus, Brazilian Tensile Strength and Point Load Strength Index was assessed for three varieties of a calcarenite. To this aim, the corresponding mechanical tests and Magnetic Resonance Imaging technique were applied during different time intervals in specimens prepared with different Sr values through two different wetting procedures: (1) the oven drying of saturated samples and (2) the water immersion of dry samples. In general terms, the results showed that for small Sr values (≤50%) the specimens wetted using the drying process exhibit greater mechanical properties reductions than those moistened through the immersion process while for higher Sr values (>50%) the decreases are quite similar for both wetting procedures. As a consequence, different negative exponential functions can be used to describe the relationship between water content and mechanical parameters of calcarenites depending on the wetting procedure used. These results can be explained by the different water distributions inside the partial-saturated specimens and the main involved water-weakening mechanisms. Additionally, slightly different correlation functions between the mechanical parameters were established for specimens moistened using each of the wetting processes.This research was supported by the Vice-rector of Research and Knowledge Transfer of the University of Alicante through predoctoral grant FPUUA53-2018 and projects UAUSTI18-21, UAUSTI19-25, UAUSTI20-20, UAEEBB2018-09 and GRE18-15 and by the Spanish Ministry of Economy and Competitiveness (MINECO) through the project TEC2017-85244-C2-1-P

High-Performance Eco-Efficient Concrete

This book is dedicated to “High-Performance Eco-Efficient Concrete” and concrete fatigue behavior, more sustainable construction materials, capable of complying with quality standards and current innovation policies, aimed at saving natural resources and reducing global pollution. The development of self-compacting concretes with electric arc furnace slags is a further achievement. In addition, the technical and economic viability of using coarse recycled aggregates from crushed concrete in shotcrete, enhanced quality and reduced on-site construction time are the basic features of prefabricated bridge elements and systems, biomass bottom ash as aluminosilicate precursor and phosphogypsum were discussed. On the other hand, basalt fiber improving the mechanical properties and durability of reactive powder concrete, alkali-activated slag and high-volume fly ash and the potential of phosphogypsum as secondary raw material in construction industry, the effects of fly ash on the diffusion, bonding, and microproperties of chloride penetration in concrete were studied. Increasing amounts of sustainable concretes are being used as society becomes more aware of the environment. Finally, the circular economy as an economic model of production and consumption that involves reusing, repairing, refurbishing, and recycling materials after their service life are presented in this book

Proceedings of FORM 2022. Construction The Formation of Living Environment

This study examines the integration of building information modelling (BIM) technologies in operation & maintenance stage in the system of managing real estate that helps to reduce transaction costs. The approach and method are based on Digital Twin technology and Model Based System Engineering (MBSE) approach. The results of the development of a service for digital facility management and digital expertise are presented. The connection between physical and digital objects is conceptualized

Stability of dams constructed on problematic substrates

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Dissolution of soluble substrates such as gypsum presents a major hazard to dams in many parts of the world. This research simulates hypothesised conditions beneath the Mosul Dam, northwest Iraq, where collapse of a karstic system associated with continuous fresh water supply from its massive reservoir water is a recognised problem. The gypsum substrates at Mosul Dam vary in purity and thickness. Experimental work used gypsum rocks and gypseous soils. Gypsum rocks from northern Iraq and similar rocks from Bantycock gypsum mine, UK, were analysed for short-term mechanical response following immersion (5 to 50 weeks) and long-term loading during immersion (maximum 50 weeks). New experimental devices were developed from a conventional oedometer. Cylinder samples (NX, standard diamond drill core size = 54mm diameter, length/diameter ratio equal to 2.5) provided a proxy for massive gypsum strata, while thin samples (NX = 54mm in diameter, 20mm thickness) represented thin layers and lenses. Rectangular bar samples (240 x 40 x 20 mm and 140 x 40 x 20 mm) were tested for short-and long-term mechanical four-point bending behaviour. Samples were permanently submerged at a variety of water pressures, with the influence of groundwater recharge and flow on dissolution simulated by regular changes of water. Stress on each sample was progressively increased to a maximum of 2688 kPa. Small increases in strain were recorded by the end of each test but no failures occurred within 60 days of tests. However, notable failure due to water pressure and axial stress over long time periods of 166 and 238 days occurred. Visible physical changes were observed, notably a decrease in sample mass and volume. Similar change was recorded in ultrasonic velocities. These indicate that gypsum collapse risk beneath dams requires prolonged exposure to dissolution. Gypseous soils from Iraq and similar artificially-prepared soils were also tested. Gypseous soil samples (diameter = 50mm and length = 20mm) and box model strata results showed that gypseous soils are significantly weakened by dissolution over 15 weeks and 50 weeks respectively. Dams built on gypsum substrates are likely to experience ongoing weakening of their foundations, with a progressively increasing risk of failure. This is expected to be enhanced for dams with a large and deep reservoir that induces high ground water pressure.This study is funded by the Ministry of Higher Education and Scientific Research, Scholarship & Cultural Relations Directorate, Iraq