Durability Of Concrete Constructions Research Articles

Performance of Fine Aggregate Replaced Pond Ash on strength of Concrete

There is a great demand for the concrete, the second largest consumed material and concrete making materials, for constructions due to stimulated growth of infrastructure worldwide. This lead to the scarcity of natural resources, resulting in creating vast interest in the research area to look for alternative materials which could satisfy both strength and performance criteria of concrete constructions. Pond ash, a waste product of thermal power plants, is one such material, that can be adopted as a suitable material as a fine aggregate in concrete, replacing natural sand partially or fully. Encouraging the usage of such a waste material as constituent in concrete so as to address the issues related to its disposal, environmental and ecological problems, is a social responsibility of researchers, thus contributing to 3Rs-Reduce Reuse and Recycle, there by promoting sustainable construction. It is commonly thought that as inert filter, fine aggregate has a very little effect on the finished concrete properties. However fine aggregate (natural sand or alternative material) and its characteristics play a substantial role in controlling the workability, strength, and durability of concrete constructions. Thus its detailed characterization is essential to boost the confidence of user. So in this report behavior of pond ash is studied. Change in compressive strength and slump values are studied.1. Thirty six concrete matrices were designed with 0, 10, 20, 30, 40 and 100 percent pond ash by replacing fine aggregate.2. The concretes of M20 with 0 percent pond ash and 100 percent fine aggregate shows compressive strength at 28 days curing 89.51 percent higher than conventional comparison mixes respectively.3. The slump values got on decreasing from 50mm for 0 percent pond ash to 0mm for 100 percent pond ash.

Effect of temperature on pozzolanic reaction of Tunisian clays calcined in laboratory

The use of natural calcined clay as supplementary cementitious materials for the replacement of a portion of cement has become increasingly interesting. It is used for reducing the cement content in mortars and concrete production and also for improving strength and durability of concrete construction. In this context, the objective of this study was to make calcined clay in laboratory using two Tunisian clays burnt at 600, 700 and 800 °C and to study the effect of temperature on Pozzolanic reaction in terms of physical, mechanical and microstructure properties. Here, we studied the thermal and chemical properties, mechanical compressive strength of mortars, electrical conductivity as well as the physical properties, namely Blaine specific surface area, average particle diameter, pycnometer density, to evaluate its pozzolanic effect by substitutions of cement (5, 10, 15 and 20%). The results show the beneficial effect of adding calcined clay at different temperatures of calcinations on these properties. Besides, the average particle diameter increased with temperatures which agglomerate the particles. The Blaine specific surface area of calcined clay exceeded that of cement. Furthermore, the substitution of cement by calcined clay enhanced the compressive strength. All samples showed the development of strength between 28 and 90 days.

USAGE OF CALCIUM CARBONATE BIODEPOSITION IN MODIFICATION OF CEMENTITIOUS COMPOSITES

Biodeterioration of construction materials is an undesired phenomenon, generating high costs of constraction repairs. On the other hand, occurrence of some bacteria can affect prevention and self repair of fractures formed in concrete. Biodeposition is an effective solution for increasing compressive strength of concrete, extending durability of concrete constructions and renovating limestone elements in facades of historic buildings.

Avaliação da penetração de cloretos em elementos de concreto na cidade de Pelotas/RS

Esta pesquisa tem como objetivo verificar a compatibilidade de um modelo de previsão de vida útil existente com a penetração de cloretos em elementos de concreto expostos na cidade de Pelotas/RS. Para tanto, foram expostos corpos-de-prova em diferentes locais da cidade por um período de 16 meses, sendo aplicada a solução de nitrato de prata para determinação da profundidade de cloretos. Foi utilizado o modelo de Bob (1996), para comparação e análise dos resultados. Foram encontrados valores significativos de cloreto nos elementos e um potencial do modelo aplicado em descrever o comportamento da profundidade de cloretos ao longo do tempo, apesar das diferenças encontradas.

Concrete durability under different circumstances based on multi-factor effects

Concrete durability has become a hot research field in civil engineering. Concrete structures suffer salt-erosion damage to different degrees in the semi-arid region of North China. The environmental condition is one of the important factors affecting the durability of concrete constructions. To realize fully the interaction between various environmental factors, this paper researched concrete durability in the salt environment under combined actions (immersing, freeze–thaw cycles, and wet–dry cycles). According to the laboratory test data, the concrete-durability degradation law under coupling-effect factors was investigated. The results show that concrete's compressive strength decreases with the increase of salt concentration and immersion time. No matter what the environmental conditions were, the compressive strength-loss ratio increased with the test time. The compressive strength-test results indicate that sodium sulfate has the strongest corrosive effect on concrete durability, followed by calcium chloride, with sodium chloride having the weakest corrosion. Compared with the other two environmental factors, the wet–dry cycle is the key factor affecting concrete durability. Therefore, in engineering practice, the influence of environment conditions on the strength and durability of concrete should be taken into full consideration, especially in the wet–dry environment with salt conditions.

Sulfate Attack on Different Types of Concrete in Media Simulating Sewer System

The degradation of concrete due to ingress of sulfate ions from the environment plays an important role in the durability of concrete constructions. Microbiologically induced concrete corrosion (MICC) damages especially sewage collection systems. The most rapid cases of deterioration always occur in areas with elevated H2S concentrations, moisture, and oxygen in the atmosphere. During the MICC, the pH of the surface of concrete sewer pipes is reduced and it may lead to the steel depassivation and results in the corrosion of steel reinforcement. Damage due to a sulfate interaction can result in a cracking and softening, with a loss of strength of concrete. The formation of ettringite (AFt) from gypsum (forming by reaction of sulfate anion with calcium hydroxide) and C3A via monosulfate (AFm) is the main chemical reaction of sulfate attack on concrete. Ettringite and gypsum have considerably larger volume than initial compounds, which leads to increased pressure in concrete. This paper is focused on the sulfate attack on fine-grained concrete where the effect of 0.5% sulfuric acid, simulating MICC, and a solution simulating sewage water has been investigated on changes of the pH, content of sulfates and the porosity in various types of concrete. The aim of this study is to compare the changes in different types of concrete during the sulfate attack in two kinds of medium represented the bottom part of pipelines (waste water) and the sewer crown (0.5% H2SO4). It was found, that after 1 year in 0.5% H2SO4, a visible degradation of surface occurs in all investigated types of concrete. Samples over the year in waste water became dark. Concentration of sulfates in all studied types of concrete increased six times at least after one year sulfuric acid attack and also the reduction of the pH of their aqueous leaches was determined. The solution simulating sewage water did not cause such changes.

Study of Fine-Grained Composites Exposed to Sulfuric Acid and Sodium Sulfate

The degradation of concrete due to ingress of sulfate ions from the environment plays an important role in the durability of concrete constructions, especially in sewage collection systems where concrete sewer pipes are exposed to sulfates from waste water and from biogenic activity of bacteria. During this process the pH of the surface of concrete sewer pipes is reduced and it may lead to the steel depassivation and results in the corrosion of steel reinforcement. Damage due to sulfate interaction can result in the cracking and softening, with loss of strength of concrete. This paper is focused on the sulfate attack on fine-grained concrete where the effect of one-year contact of 0.5% H2SO4, and 5% Na2SO4 on changes of pH and content of sulfates in 7 types of concrete has been analyzed. It was found that after one year of sulfate attack on concrete, significant growth of content of sulfates is observed in the lowermost layer of the samples. Samples treated by 5% Na2SO4 contain slightly more sulfates in the upper layers than samples treated by sulfuric acid. The reduction in pH of aqueous leaches occurred in all layers of the samples. However, even in the lower layers of the samples, the reduction of pH below 9.5 did not turn up (except for SRS sample), and thus the conditions for the depassivation of reinforcement were not met.

Internal cracking and transport properties in damaged concretes

The durability of concrete constructions is strongly related with the transport of fluids through the material. The presence of pores and cracks increases the permeability of the material, enhancing the ingress of aggressive agents that contribute to the material degradation. In this sense the internal structure is decisive, mainly the characteristics of the mortar matrix and the aggregates of greater size and its interfaces. In this work the incidence of different types of cracks on the transport properties is analyzed, considering several cases of degradation: concretes damaged by exposure to low humidity conditions or to high temperatures (150 and 500°C), and a concrete affected by alkali-silica reaction (ASR). The characterization of the internal structure was made at the mesostructural level through the assessment of the density and width of cracks; as transport properties the water absorption, capillary absorption, water penetration and coefficient of water permeability were considered. As expected the width, the density and the type of fissures had a strong impact on the transport properties, however each variable will have a higher or lower incidence depending on the transport mechanism involved. In concretes damaged by drying shrinkage the permeability increased steadily with the crack density, however, the capillary absorption after reaching a maximum decreased for cracks of greater width. At the same time in concrete damaged by ASR, differences were found in the water penetration test in accordance with the crack orientations which were not verified in the values of the coefficient of permeability.

Effect of Cement Replacement, Content, and Type on the Durability Performance of Fly Ash Concrete in the Middle East

Abstract The low durability of concrete construction in the Middle East caused by corrosion of reinforcement, sulfate attack, environmental cracking, and aggregate-cement reactivity necessitates that mix design techniques be formulated to yield dense and impervious concrete with as little heat of hydration as possible; it should also have enhanced resistance to salt attack and possible cement-aggregate reactivity. These objectives present fly ash as a potentially useful admixture from the standpoint of improving the durability of concrete construction in the aggressive service environment of the Gulf seaboard. This investigation presents data on the strength, general quality, and durability performance of fly-ash portland-cement concrete against sulfate/chloride attack. The variables used for this study are fly ash additions as cement replacement from 0 to 40%, cement factors of 300, 360 and 450 kg/m3 (500, 600, and 750 lb/yd3) and tricalcium aluminate (C3A) phase ranging from 0 to 9.5%. Results show that 20% replacement by fly as shows the best performance in terms of rate of strength gain, ultimate strength, absorptive characteristics, and resistance to sulfate/chloride attack. The strength gain is superior in lean mixes, and the effect of fly ash addition on sulfate resistance of concrete is more pronounced for higher C3A cements. An increase in the cement factor without attendant changes in water/cement ratio does not necessarily provide better durability performance.

Durability of Concrete Construction — 50 Years of Progress

In 1925, many of the problems of concrete durability were recognized. It was also recognized that concrete that had endured for 2,000 yr existed. The need for recognizing the destructive agencies and discovering satisfactory remedies was appreciated. After 50 yr, progress in understanding factors causing deterioration of concrete has been such that deterioration can be prevented provided that the cause can be anticipated and appropriate measures taken. Different precautions are needed for different causative factors that may be destructive agencies. Deterioration from frost action, chemical reactions of alkalies and soluble silica in the aggregates, sulfate attack, delayed hydration of free lime or magnesia, or both, in the cement, expansion of certain kinds of aggregate particles caused by chemical reactions other than those with alkalies, surface contraction due to drying, and solution (leaching) can be prevented by other precautions.