Moisture Distribution In Concrete Research Articles

An improved ring test to assess cracking resistance of concrete under restrained shrinkage

Self-restraint caused by differential shrinkage along the radius of a concrete ring has great driving effect on the restrained cracking in the traditional ring test. In order to estimate cracking potential of concrete under restrained shrinkage, i.e. steel ring restraint effect, an improved circular/elliptical ring test was proposed by pre-setting a 6 mm long real crack at the inner circumference of the concrete specimen. Meanwhile, a numerical study based on fracture theory was conducted to investigate the cracking mechanism of the improved ring test. By introducing the fictitious crack model, the crack initiation age and propagation process in the ring specimen were simulated using the initial fracture toughness-based cracking criterion. The driving forces of the shrinkage cracking, provided by self-restraint and steel ring restraint, were analyzed and the influence of the pre-set crack length on the cracking age was discussed. The results indicated that, different from the traditional ring test, the shrinkage crack firstly initiated from the pre-set crack and then unstably propagated toward the outer circumference of the concrete in the improved method. In the crack propagation process, the self-restraint provided cracking insistence rather than driving force on the shrinkage cracking due to the bending effect along the radial direction caused by non-uniform moisture distribution in concrete. Therefore, the driving force of the shrinkage cracking was totally provided by the steel ring restraint and would overcome the cracking resistances from concrete material and non-uniform shrinkage. Furthermore, the advantage of the elliptical geometry in increasing the restraining level was still available for the improved ring test with a pre-set crack, which could make the shrinkage cracking occur in advance and enhance the steel ring restraint.

Vertical water transport model in concrete based on the coupled effects of the capillarity, gravity and evaporation

A novel vertical water transport model in consideration of the capillarity, gravity effect and evaporation was proposed, and the corresponding finite difference method was recommended to determine the moisture distribution in concrete. The amounts of water absorption and water loss of concrete surface with time were measured, and the distributions of relative humidity (RH) and temperature in concrete were also tested under different environment conditions. Moreover, the numerical simulation was used to elucidate the phenomena of rot, damp and saltpetering in the dry-wet region of concrete column contacting with soil or water. The results showed that the variations of RH and temperature in concrete along the vertical height from liquid level accord well with a Bolztmann function. The relationship between the water absorption and time expresses as an exponential function, but it is a Logistic function between water loss and time. The moisture distribution in concrete observably changes with the vertical height from liquid level and distance from concrete surface, which is mainly caused by the dynamic equilibrium between the absorbed water by capillarity and gravity, and the evaporated water by evaporation. The significant change region of RH along the vertical height of concrete surface was closely related with concrete strength grade and external environment’s RH, and the corresponding values for C20, C30 and C40 are about 20 cm∼30 cm and 10 cm∼20 cm, respectively. The RH and temperature of concrete surface differ from that of external environment, which changes the traditional lopsided view considering the external environment as the micro environment in concrete. The pore characteristic for different concrete strength grade results in a significant variation of the moisture distribution in concrete, which expresses as the similar change trend but different value.

Moisture determination of concrete panel using SAR imaging and the K-R-I transform

Moisture content inside concrete affects the properties and behaviors of Portland cement concrete. It also indicates the likelihood of structural damages (e.g., steel corrosion) in reinforced and prestressed concrete structures. While several laboratory techniques are available for moisture determination, it is a challenging task to estimate the moisture content of concrete in the field without using embedded moisture sensors. In this paper, synthetic aperture radar (SAR) imaging and the K-R-I (curvature-area-amplitude) transform were applied to a concrete panel specimen (water-to-cement ratio = 0.45) for moisture determination. A 10.5 GHz center frequency radar system was used to generate SAR images of the concrete panel at various moisture levels from 0% to 3.85% (by mass). Quantitative analysis of SAR images was carried out by the K-R-I transform to understand the simultaneous change of SAR amplitude and shape at different moisture levels. It was found that integrated SAR amplitude and average maximum SAR amplitude both increase nonlinearly with the increase of moisture content in the concrete panel. Spatial distribution of SAR amplitudes can be used to indicate subsurface moisture distribution in concrete. The area-amplitude (R-I) curve of SAR images quantifies the relationship between moisture content and its distribution.

Experimental research and mechanism analysis on chloride ingress at different concrete zone along altitude in marine environment. Part 1. Moisture distribution

The moisture distributions in concrete of different zones are different in marine environment. The variations of moisture distribution during drying and wetting were analyzed in this paper. A laboratory test system that whole piece of real concrete was subjected to an environment close to the real marine environment was developed and used to simulate the real marine environment, by which the variations of moisture distribution in concrete of different zones along elevated altitude were studied. The test results reveal that the influential depth of moisture transport (IDMT) and the stability moisture content (StMC) in concrete of different zones are variable. The IDMTs in concrete of splash and tidal zones are larger than those of other zones. IDMT changes along elevated altitude, and the peak value of IDMT appears near the top water line of tidal zone which is the key region of durability design and maintenance.

CO2 uptake potential due to concrete carbonation: A case study

The cement manufacturing process accounts for about 5% CO2 (carbon dioxide) released into the atmosphere. However, during its life cycle, concrete may capture CO2 through carbonation, in order to, partially, offset the impact of its production. Thus, this paper aims at studying the CO2 uptake potential of the Itaipu Dam due to concrete carbonation of such material. So, 155 cores were extracted from the concrete dam in different points to measure carbonation depth. In order to evaluate its influence on carbonation, the measurement of internal moisture distribution in concrete was also carried out. The results have shown that carbonation takes part of the whole dam area, indicating CO2 uptake potential. Up to the present moment, 13,384 tons of CO2 have been absorbed by concrete carbonation of the Itaipu Dam.

Moisture distribution in concrete subjected to rain induced wetting-drying

A rational estimation of moisture distribution in structural concrete is vital for predicting the possible extent and rate of progression of impending degradation processes. The paper proposes a numerical scheme for analysing the evolution of moisture distribution in concrete subjected to wetting-drying exposure caused by intermittent periods of rainfall. The proposed paradigm is based on the stage wise implementation of non-linear finite element (FE) analysis, with each stage representing a distinct phase of a typical wet-dry cycle. The associated boundary conditions have been constituted to realize the influence of various meteorological elements such as rain, wind, relative humidity and temperature on the exposed concrete surface. The reliability of the developed scheme has been demonstrated through its application for the simulation of experimentally recorded moisture profiles reported in published literature. A sensitivity analysis has also been carried out to study the influence of critical material properties on simulated results. The proposed scheme is vital to the service life modelling of concrete structures in tropical climates which largely remain exposed to the action of alternating rains.

Single-point magnetic resonance imaging (MRI) of cement based materials

The use of Magnetic Resonance Imaging (MRI) as a tool for non-destructive testing of moisture distribution and moisture migration in concrete and mortar is described. MRI spatially resolves in one, two, or three dimensions, the evaporable water content in cement based materials as a function of time, treatment or processing conditions. The use of the technique is demonstrated through studies of drying and freezing behavior in partially saturated materials. Studies of one-dimensional drying of concrete cylinders show a clear dependence of the capillary and diffusive drying rates on moist curing time and water-cement ratio. Three-dimensional imaging is demonstrated to visualize the internal moisture distribution in concrete. MRI experiments may spatially resolve the freezing behavior of concrete, and thereby determine the occupied pore size distribution. In addition two-dimensional time resolved imaging of a propagating freezing front into a model concrete wall is demonstrated. Finally a modification of the basic methodology is described which permits imaging of nuclei other than hydrogen. Chloride and sodium distribution in mortar, associated with salt water invasion, may thereby be determined.