Cracking In Concrete Elements Research Articles

Avaliação do pó de vidro na mitigação da reação álcali-sílica (RAS)

Abstract The alkali-silica reaction (ASR) is one of the problems that can compromise concrete durability, as the chemical reactions between the reactive aggregate and concrete pore solution, specifically sodium (Na+), potassium (K+), calcium (Ca2+) and hydroxyl (OH-) in the presence of moisture, trigger expansion and cracking of concrete elements. The use of pozzolanic materials, such as finely ground glass powder (particles smaller than 75μm), to partially replace cement has been widely studied and has demonstrated beneficial results. However, because the behavior of pozzolans towards ASR is not completely understood yet, this work evaluates the effect of incorporating ground glass powder into cementitious composites against ASR. To this end, 8% silica fume was used as a control admixture, and four levels of glass powder (10, 20, 30, and 50%) were incorporated into the cementitious mixture to partially replace cement. Expansion tests were carried out in accordance with NBR15577-4 (ABNT, 2018) on mortar bars using the accelerated test method to assess the mitigation of expansions. The results show that the expansions caused by ASR decreased with the increasing content of glass powder in the cement mixtures. Furthermore, only the 50% level reduced the expansions to a safe value according to the Brazilian standard.

Automated Measurement of Geometric Features in Curvilinear Structures Exploiting Steger's Algorithm.

Accurately assessing the geometric features of curvilinear structures on images is of paramount importance in many vision-based measurement systems targeting technological fields such as quality control, defect analysis, biomedical, aerial, and satellite imaging. This paper aims at laying the basis for the development of fully automated vision-based measurement systems targeting the measurement of elements that can be treated as curvilinear structures in the resulting image, such as cracks in concrete elements. In particular, the goal is to overcome the limitation of exploiting the well-known Steger's ridge detection algorithm in these applications because of the manual identification of the input parameters characterizing the algorithm, which are preventing its extensive use in the measurement field. This paper proposes an approach to make the selection phase of these input parameters fully automated. The metrological performance of the proposed approach is discussed. The method is demonstrated on both synthesized and experimental data.

A weather data analysis method to mitigate and prevent plastic shrinkage cracking

Placing fresh concrete in high evaporation conditions can increase the permeability and risk of plastic shrinkage cracking in concrete elements. Prevention measures can be time-consuming and expensive and are often neglected or incorrectly applied. This study proposes a data analysis method to identify the best time for concrete placement, most effective active curing measures, limits on weather condition for concrete placement and adequate testing conditions from location-specific weather data to reduce and mitigate the adverse effects of extreme weather concreting. The aim of this study is to characterise the evaporativity of a region and identify common trends that may be useful for planning concrete projects. The method can be applied to weather data from any location to produce more specific plastic shrinkage crack prevention and extreme weather concreting guidelines. To show the potential of this method, it is applied to four geographically and meteorologically different locations. The selected locations have a hot and dry climate, but the method can also be applied to a cold and dry climate which can, in some cases, produce even higher evaporation rates. The results indicate that for the selected locations specific active curing measures should be rigidly enforced throughout the year and that additional passive prevention measures are required in summer months. The necessity for additional passive prevention can be significantly mitigated by selecting a placement time with a lower evaporation rate.

Evaluation of polyurethane resin injection for concrete leak repair

The aim of this study is to evaluate the effectiveness of water leakage treatment using polyurethane resin injection for concrete structure elements. Water leakage may have destructive effects on building structures. Leaks may be attributed to several factors, such as the use of an inadequate waterproofing system, inadequate design, poor concrete quality, and poor workmanship.A wide range of techniques and products are employed to control water intrusion, including resin injection, which is among the methods commonly used for resolving leakage in waterproofing systems. The aforementioned techniques and products also provide special solutions for other construction problems. In this study, the effectiveness of using resin injection to stop water leakage is investigated. As part of the experimental work, two water tanks are modelled to simulate actual field conditions. The tanks are filled with pumped water, and three measured water pressure values are investigated to determine the effectiveness of resin injection method. The water pressure is gradually increased up to 3 bar (43.5 psi) for three days, and relevant pressure reductions are determined in each case. The results indicate that the ability of concrete elements to resist water flow is inadequate when a waterproofing system is not employed (Case 1); however, concrete permeability is slightly reduced when waterproofing materials are used (Case 2). More specifically, the use of polyurethane resin injection can substantially stop water leaks (Case 3). Polyurethane resins are designed to expand with water to permanently block the passage of water through cracks or voids. Their fast expansive reaction with water forms a tough and flexible/elastic foam. The analysis demonstrates the reduction in concrete permeability after the application of polyurethane resin injection. The results obtained in this research can be utilised as a solution to stop water leaks and cracks in concrete elements, such as basement walls, manholes, tunnels, storm sewers, retaining walls, seawalls, dams, below-grade parking decks, water treatment tanks, elevator pits, box culverts, below-grade vaults, walls, pits, and floors.

Condition Assessment of Cementitious Materials Using Surface Waves in Ultrasonic Frequency Range

Surface waves propagating in a medium provide information about the mechanical properties and condition of the material. Variations in the material condition can be inferred from changes in the surface wave characteristics. Multichannel analysis of surface waves (MASW) is a well-established surface wave method used for determination of the shear-wave profile of the soil layers near the surface. The MASW test configuration is also applicable to assess the condition of construction materials using appropriate frequency range. Previous studies on the detection of surface-breaking cracks in concrete elements, using the dispersion and attenuation of ultrasonic waves, were successful; however, a complete damage assessment of the whole element was not in the scope of these studies. In this study, different wave characteristics, such as Rayleigh wave velocity, wave attenuation, and phase velocity dispersion, are investigated to evaluate their sensitivity to the damage in a medium. The condition of a test specimen, which is a half-space medium made of cement and sand, is evaluated using ultrasonic transducers for different damage cases. The recorded signals are processed using the Fourier and wavelet transforms to determine the surface wave characteristics. A new dispersion index (DI) is introduced, which represents the global correlation between the dispersion of phase velocity and damage level. All features are found to be capable of reflecting the damage in the test medium with different levels of sensitivity. Among the investigated parameters, the proposed dispersion index shows high sensitivity and linear correlation with the damage.

Wireless Crack Detection in Concrete Elements Using Conductive Surface Sensors and Radio Frequency Identification Technology

This paper describes the results of an experimental study that uses radio frequency identification (RFID) technology to detect cracking in concrete elements. A RFID-based sensor is used to monitor the change in electrical resistance that occurs in conductive materials applied to the surface of the concrete. When the concrete substrate is strained, the conductive material at the surface is stretched, and its electrical resistance increases. If the concrete substrate is strained to the point where it cracks, the conductive material at the surface also cracks, causing its electrical resistance to increase by orders of magnitude. This paper describes how this increase in electrical resistance attributable to cracking can be detected wirelessly by RFID technology. To experimentally illustrate the application of this technology, an RFID-based sensor and conductive surface materials are used to detect cracking in the restrained ring test. The experimental results indicate that this technology can be easily implemented and successfully used for wireless crack detection in concrete and reinforced concrete members. The technology that is described in this paper is not limited to the laboratory environment and can be easily extended to field applications.

Restrained Shrinkage Cracking in Concrete Elements: Role of Substrate Bond on Crack Development

Several specimen geometries have been used to assess restrained shrinkage-cracking behavior of concrete materials. This paper used a series of restrained slab tests to illustrate the importance of specimen geometry on the restrained shrinkage cracking behavior. While restraint was provided along the base of the slab, a portion of the slab was left unbonded to the base in the center of the specimen. The length of this unbonded portion was varied to demonstrate its impact on the age of cracking and crack width that occurred. The age of cracking was measured using visual analysis, image analysis, conductive surface coating, and acoustic emission. Whereas image analysis and conductive paint detect cracks only after they appear on the surface, acoustic emission also provides information on damage development before the cracks were visible. Cracking occurred in a less stable fashion in slabs with a larger unbonded region. The larger unbonded length in a slab caused wider cracks to appear at an earlier age than in a slab with a smaller unbonded region.

Interactions between shrinkage reducing admixtures (SRA) and cement paste's pore solution

Shrinkage reducing admixtures (SRA) have been developed to combat shrinkage cracking in concrete elements. While SRA has been shown to have significant benefits in reducing the magnitude of drying and autogenous shrinkage, it has been reported that SRA may cause a negative side effect as it reduces the rate of cement hydration and strength development in concrete. To examine the influence of SRA on cement hydration, this study explores the interactions between SRA and cement paste's pore solution. It is described that SRA is mainly composed of amphiphilic (i.e., surfactant) molecules that when added to an aqueous solution, accumulate at the solution–air interface and can significantly reduce the interfacial tension. However, these surfactants can also self-aggregate in the bulk solution (i.e., micellation) and this may limit the surface tension reduction capacity of SRA. In synthetic pore solutions, SRA is observed to form an oil–water–surfactant emulsion that may or may not be stable. Specifically, at concentrations above a critical threshold, the mixture of SRA and pore fluid is unstable and can separate into two distinct phases (an SRA-rich phase and an SRA-dilute phase). Further, chemical analysis of extracted pore solutions shows that addition of SRA to the mixing water depresses the dissolution of alkalis in the pore fluid. This results in a pore fluid with lower alkalinity which causes a reduction in the rate of cement hydration. This may explain why concrete containing SRA shows a delayed setting and a slower strength development.