Interior Of Concrete Research Articles

Effect of clay content on concrete properties

The presence of clay in aggregate is frequently associated with the deterioration of concrete properties. The objective of this study was to investigate the effects of varying clay contents on the mechanical properties, freeze-thaw resistance, permeability and water absorption behavior of concrete. Additionally, the differences in the permeability, and water absorption behavior of the surface layer and interior of concrete were comparatively analyzed using self-designed tests. The results indicate that the presence of a minimal quantity of clay did not diminish the compressive strength and static compressive modulus of elasticity of concrete. However, it did result in a reduction in the tensile properties and durability of concrete. Furthermore, the mechanical properties, freeze-thaw resistance, and anti-permeability of concrete were significantly diminished when the clay content reached 1.6%. Furthermore, this study proposed an innovative evaluation method for dividing the water absorption behavior of concrete into three stages, which more accurately reflected the trend of water absorption behavior in concrete. It was found that the sorptivity and permeable porosity of concrete in the three stages exhibited a strong correlation. The presence of clay increased the sorptivity and permeable porosity of concrete, with the most pronounced effect observed in the initial water absorption stage. Moreover, the permeable porosity of the interior of concrete was found to be reduced in comparison to that of the surface layer of concrete at all ages with varying clay contents, with the reduction ranging from 10.7% to 14.7%. In practical engineering construction, it is recommended that the clay content be kept within reasonable limits, and the effect of the clay content on the properties of the surface layer of concrete be given greater attention.

Mechanical and seepage characteristics of polyvinyl alcohol fiber concrete under stress-seepage coupling

This study presents an experimental investigation of the coupled stress and seepage water pressure loading test conducted on polyvinyl alcohol (PVA) fiber concrete, which had undergone salt attack freeze-thaw (F-T) cycles. This study delves into the influence of the number of salt attack F-T cycles, as well as the magnitude of seepage water pressure, on the triaxial compression seepage mechanical properties and permeability evolution of the specimens. Additionally, the nuclear magnetic resonance (NMR), scanning electron microscope (SEM) and X-ray diffraction (XRD) test results were analyzed, revealing that sodium sulfate solution penetrates the interior of PVA fiber concrete and reacts with cement stone to form ettringite and gypsum, which initially fills and compacts the pore structure. The increased production of such compounds causes pore structure to expand, with the maximum number of mesopores and macropores increasing by 115.5%. Macroscopically, it was observed that the mass and peak strength of the specimens increased at the beginning of the cycle, and the initial permeability decreased. However, the opposite phenomenon occurred after 15 cycles. When seepage water pressure was increased from 1 MPa to 3 MPa, the crack initiation stress, crack damage stress, and peak stress of the specimens decreased by 13.1%, 16.9%, and 15.6% on average, respectively, and the initial permeability increased by 69.3% on average. The deformation process of PVA fiber concrete under stress-seepage coupling loading was divided into five stages, including the initial compaction stage, elastic deformation stage, crack initiation and stable propagation stage, crack unstable propagation stage, and post-peak deformation stage. Correspondingly, the permeability exhibited a rapid decline, followed by a relatively stable phase, a slow rise, a rapid rise, and a continuous increase. Besides, the relationship between permeability and volume strain in compression and expansion stages was clarified.

Environmentally friendly super-slippery concrete with anti-corrosion and anti-fouling properties

Due to superhydrophilicity and porosity, the concrete structure of buildings in marine engineering is easily corroded and polluted. Superhydrophobic concrete has been studied and applied to alleviate this problem; however, the poor stability under high pressure and in contact with foulings hampers its wide application. To overcome the above challenges, we develop an environment-friendly and inexpensive super-slippery concrete (SS-concrete) by injecting oil into the interior and outer surface of the superhydrophobic concrete (SH-concrete). The impendence of SS-concrete is 3 orders of magnitude larger than that of ordinary concrete (O-concrete), indicating that the corrosion resistance of concrete has been significantly improved. Moreover, the stable protective oil layer of the SS-concrete prevents the infiltration and adhesion of water, ice, oils, ink, milk and even bacteria, showing excellent anti-fouling ability. Therefore, the SS-concrete may have great potential application in the concrete-based buildings in marine engineering field.

Effect of Moisture Distribution on Velocity and Waveform of Ultrasonic-Wave Propagation in Mortar.

Considering that the ultrasonic method is applied for the quality evaluation of concrete, this study experimentally and numerically investigates the effect of inhomogeneity caused by changes in the moisture content of concrete on ultrasonic wave propagation. The experimental results demonstrate that the propagation velocity and amplitude of the ultrasonic wave vary for different moisture content distributions in the specimens. In the analytical study, the characteristics obtained experimentally are reproduced by modeling a system in which the moisture content varies between the surface layer and interior of concrete.

A critical review on the effect of organic acids on cement-based materials

Ingression of acids into concrete structure arrests its long-term durability by the progressive degradation of the highly alkaline cementitious materials. Acid attack results in the decalcification of hydration products leading to higher inherent porosity and both micro-macro cracks, providing a path for the passage of aggressive ions into the interior of concrete. Amplification of agriculture and food industries such as the breeding, dairy or sugar industries produce large quantities of effluents that are the major sources of organic acids. These effluents have complex acidic compositions leading to serious degradation of structures made for their production, collection, storage and treatment. New binder systems that are capable of proposing extensive long term durability in aggressive acidic environment and also being a sustainable option need to be evolved. From earlier studies, application of various binder systems containing materials such as fly ash, ground granulated blast furnace slag, silica fume, bagasse ash etc. has an influence on the hydration products, micro-structural and macro-structural changes in cement-based materials when subjected to aggressive acidic media, thus enhancing the performance and durability of concrete structures. This paper outlines the basic mechanism of organic acid attack and highlights the influence of various binder systems on the alteration of degradation kinetics when exposed to various organic acids.

Superhydrophobic anticorrosive coating for concrete through in-situ bionic induction and gradient mineralization

Owing to the inherently multi-scale hydrophilicity of concrete, water and corrosive ions that may cause deterioration can easily adsorb to the surface through capillarity, and further penetrate into the interior of concrete. Superhydrophobic surface is one of the best choices for anti-corrosion, but it faces difficulties in durability and adaptability. This study reports a facile route to fabricate superhydrophobic concrete via in-situ biomineralization of inorganic crystals CaCO3 at specific sites controlled by organic matrix. Under the bionic induction of dopamine, the multi-stage gradient structure has been fabricated on calcite crystal, in which a micro-nano composite structure has been formed on the concrete surface. The induction mechanism is explained by the density functional theory. The structure, composition and topological features of the prepared nano-coatings have been characterized by various surface analysis techniques. After modified by silane, the superhydrophobicity and hydrophobic stability of the surface has been confirmed by its large contact angle (CA = 156 ± 3°) and its stability under water, being attributed to the modified concrete voids, the surface micro/nanostructures and a silane layer on them.

Effect of steam curing on surface permeability of concrete: Multiple transmission media

Nowadays, steam curing has become an effective way to produce high early strength concrete prefabricated elements. However, this curing regime has been proved to lead to the heat damage on the microstructures and properties of concrete. Therefore, how to characterize the heat damage, and the impact of heat damage on the durability of concrete is a key issue. In this study, three treatment temperatures were employed to study the heat damage of steam-cured concrete. In addition, the surface gas permeability (SGP), water intentional spraying tests (WIS), pore structure, TG-DSC and SEM were measured to analyze the effects of curing regimes on performance of steam-cured concrete. The results indicate that there are differences in the surface and interior of steam-cured concrete, and surface permeability (SGP and WIS) can characterize these differences. Meanwhile, high temperature steam curing is detrimental to the long-term impermeability of concrete, and surface treatment can improve this phenomenon. The surface covered by geotextile has the lowest permeability and relatively dense microstructures.

Heat damage of concrete surfaces under steam curing and improvement measures

Steam curing is commonly used in the production of prefabricated elements in China. However, this curing regime has proven to have an adverse effect on the long-term performance of concrete due to heat damage effects. Steam curing (60 ℃) were compared with standard curing (20 ℃ and 90% RH), and the temperature field inside the cement pastes under two curing regimes was tested by a temperature sensor. The effects of the precuring time, water-binder ratio, surface treatment methods, mineral admixtures, forming process, and subsequent curing conditions on heat damage of steam-cured concrete were examined by capillary water absorption, pore structure and microstructure. The results indicate that there are obvious pore gradients and microstructure differences of hydration products in the surface and interior of steam-cured concrete, and the sorptivity coefficient of the surface is also higher than the internal. Prolonging the precuring time can achieve high early resistance, and surface treatment can reduce the interconnected porosity of the exposed surface. Moreover, concrete mixed with mineral admixtures can delay the hydration process of the cementitious component, which is also beneficial to reduce heat damage. The higher stiffness of the steel mold can offset part of the internal stress, which reduces the sorptivity coefficient of the steam-cured concrete. In addition, appropriate subsequent curing conditions are necessary for steam-cured concrete.

Effects of Medium Temperature and Industrial By-Products on the Key Hardened Properties of High Performance Concrete.

The aim of the work reported in this article was to investigate the effects of medium temperature and industrial by-products on the key hardened properties of high performance concrete. Four concrete mixes were prepared based on a water-to-binder ratio of 0.35. Two industrial by-products, silica fume and Class F fly ash, were used separately and together with normal portland cement to produce three concrete mixes in addition to the control mix. The properties of both fresh and hardened concretes were examined in the laboratory. The freshly mixed concrete mixes were tested for slump, slump flow, and V-funnel flow. The hardened concretes were tested for compressive strength and dynamic modulus of elasticity after exposing to 20, 35 and 50 °C. In addition, the initial surface absorption and the rate of moisture movement into the concretes were determined at 20 °C. The performance of the concretes in the fresh state was excellent due to their superior deformability and good segregation resistance. In their hardened state, the highest levels of compressive strength and dynamic modulus of elasticity were produced by silica fume concrete. In addition, silica fume concrete showed the lowest level of initial surface absorption and the lowest rate of moisture movement into the interior of concrete. In comparison, the compressive strength, dynamic modulus of elasticity, initial surface absorption, and moisture movement rate of silica fume-fly ash concrete were close to those of silica fume concrete. Moreover, all concretes provided relatively low compressive strength and dynamic modulus of elasticity when they were exposed to 50 °C. However, the effect of increased temperature was less detrimental for silica fume and silica fume-fly ash concretes in comparison with the control concrete.

Piezoelectric actuator/sensor wave propagation based nondestructive active monitoring method of concrete structures

In order to monitor the basic mechanical properties and interior damage of concrete structures, the piezoelectric actuator/sensor based wave propagation method was investigated experimentally in the laboratory using a specifically designed test setup. The energy attenuation of stress waves was measured by the relative index between the output voltage of sensors and the excitation voltage at the actuator. Based on the experimental results of concrete cube and cylinder specimens, the effect of excitation frequencies, excitation amplitude, wave propagation paths and the curing age on the output signals of sensors are evaluated. The results show that the relative voltage attenuation coefficient RVAC is an effective indicator for measuring the attenuation of stress waves through the interior of concrete.

Non-destructive tomographic energy-dispersive diffraction imaging of the interior of bulk concrete

A new tomographic technique, termed TEDDI (tomographic energy-dispersive diffraction imaging) has recently been invented by Hall et al. [C. Hall, P.Barnes, J.K. Cockcroft, S.L. Colston, D. Hausermann, S.D.M. Jacques, A.C. Jupe, M. Kunz, Synchrotron radiation energy-dispersive diffraction tomography, Nucl Instrum Methods Res, Sect B 140 (1998) 253–257; C. Hall, P. Barnes, J.K. Cockcroft, S.D.M. Jacques, A.C. Jupe, X. Turrillas, M. Hanfland, D. Hausermann, Rapid whole-rock mineral analysis and composition mapping by synchrotron X-ray diffraction, Anal Commun 33 (1996) 245–248] and applied to cementitious systems. TEDDI has notable unique features in that: • it exploits diffraction, rather than spectroscopic sensing, and therefore directly yields compositional/structural information about the sample; • the diffracting region can be made small or large depending on application, the ultimate spatial resolution being in the micron range; • with the use of energetic (20–125 keV) synchrotron beams, bulk objects such as concrete blocks can be penetrated so that the technique becomes non-destructive. We report on early tests of this technique as a means to non-destructively examine the interior of concrete prism specimens. Concrete, by definition, is a heterogeneous material because it contains coarse aggregates on a length scale of ∼1 cm. This is orders of magnitude larger than the effective penetration depth of conventional X-ray diffraction systems (typically <100 μm at 1.54 Å) which, therefore, cannot probe the interior of intact concrete specimens. It is possible to pulverize concrete, sift out the aggregates, and analyze the remaining fraction but the degree of representation of such powders is questioned since certain phases may be lost or enriched during this process; furthermore, the spatial distribution of the analyzed phases within the concrete will be lost and, with it, important information such as whether the phase in question forms in the cement paste matrix or at the aggregate interface. Even after these limitations, conventional diffraction/microscopy analysis is at best a “one shot” process in time. The TEDDI technique has the promise to avoid all these problems by enabling the examination of intact concrete specimens on the length scale of several centimeters.