Surface Condition Of Concrete Research Articles

Effects of concrete type, concrete surface conditions and wood species on interfacial properties of adhesively-bonded timber – Concrete composite joints

To optimize the bonding performance between prefabricated concrete and wood in adhesive-bonded timber-concrete composite (TCC) system, the authors conducted quasi-static shear tests on several types of TCC joints bonded with epoxy resin in this study. The experimental variables considered were (1) concrete surface conditions (i.e. sandblasted, sanded and non-treated), (2) concrete type (i.e. normal strength concrete (NSC), high strength concrete (HSC) and ultra-high-performance concrete (UHPC)), and (3) wood species (i.e. glulam GL24 made of spruce and beech wood). The test results showed that the surface treatment on NSC (sandblasted) and HSC (sanded) significantly increased the shear bond strength of the TCC joints and changed the predominant failure mode from tearing-off of mortar-facial covers into failures in concrete substrates. Upon the surface treatment, using HSC increased the shear bond strength compared with the TCC joints using NSC. The joints with UHPC predominantly failed in the adhesive/concrete interface, and adhesion between adhesive and concrete, due to that the low porosity of UHPC impeded the penetration of epoxy resin into the substrate. When being bonded with UHPC, compared with the GL24 made of spruce, the beech wood increased the shear bond strength, since the wood-failure percentage decreased in the joints using beech wood. Furthermore, bond-line areas of all types of joints were examined under an optical microscope, to reveal the morphology (i.e. profile of a glue line, glue-line thickness, and penetration of resin into substrates). It was found that epoxy used in this study with a high initial viscosity (i.e. 6000 mPa·s at 23 °C) is suitable to bond surface-treated concrete and engineered wood, from the perspectives of penetration into substrates, the thickness of glue lines, and workability during gluing processes.

Effects of steam curing regimes on the capillary water absorption of concrete: Prediction using multivariable regression models

Effects of steam curing parameters on the capillary water absorption (CWA) of concrete are investigated, and the models related to steam curing parameters for predicting the sorptivity coefficient of concrete are developed using extensive experimental database. The results show that the CWA and sorptivity coefficient of steam-cured concrete is closely related to the steam curing regimes and the surface condition of concrete. Longer precuring time or lower heating rate can reduce the CWA and sorptivity coefficient of steam-cured concrete. When the treatment time is 8 h, higher and lower treatment temperature can increase the CWA and sorptivity coefficient of concrete. When the treatment temperature is 60 ℃, the CWA and sorptivity coefficient of concrete increase with the treatment time. Highest cooling rate will lead to highest sorptivity coefficient of steam-cured concrete. The CWA and sorptivity coefficient of top surface are higher than that of side surface, and the CWA and sorptivity coefficient of surface concrete are higher than that of the interior concrete. In addition, the surface treatment methods of quadric-plastering and covering film can reduce the CWA and sorptivity coefficient of concrete. Finally, linear regression analysis and multiple nonlinear regression are employed to simulate the sorptivity coefficient of steam-cured concrete. The multivariable regression analysis method gives an explicit formula that achieves a good predictive result.

In-situ monitoring of corrosion-induced expansion and mass loss of steel bar in steel fiber reinforced concrete using a distributed fiber optic sensor

Corrosion causes mass loss of steel bars, concrete cracking, and interface degradation in reinforced concrete, highly compromising the safety and durability of civil infrastructure. This research proposes a smart reinforced concrete instrumented with a distributed fiber optic sensor for in-situ monitoring, presents an innovative method to quantify mass loss of steel bar using unique distributed sensor data, and studies corrosion-induced expansion of steel bar in steel fiber reinforced concrete. Electrochemical test and the distributed sensor data were used to understand the corrosion deterioration process of the steel-concrete composite. Effect of the steel fiber on the deterioration process is evaluated under different concrete surface conditions, and the underlying mechanisms are investigated. The results indicate that steel fibers reduced the corrosion rate of steel bars by mitigating electron transfer from the steel bar, delaying concrete cracking, and limiting the crack width. The effect of concrete surface defects shows a transition phenomenon. This research gains insights into the corrosion deterioration mechanism and strategies for improving the long-term durability of steel-concrete composite.

Detection of internal defects of concrete structures based on statistical evaluation of healthy part of concrete by the noncontact acoustic inspection method

A noncontact acoustic inspection method was developed to perform measurements from a long distance (usually about 5 to 7 m but even over 30 m) and detect internal defects (up to 10 cm in depth) of concrete structures using a long-range acoustic device and a laser Doppler vibrometer. An algorithm was also proposed to detect internal defects of concrete by combining two acoustic features, the vibrational energy ratio and spectral entropy obtained by our measurement. However, in actual concrete structures, it is difficult to distinguish a boundary between a healthy part and a defective part owing to influences such as the shape of internal defects, age-induced deterioration, and the surface condition of concrete. Therefore, we propose a method to statistically evaluate the distribution of the healthy part of concrete and extract the healthy part to identify the defective part. By this proposed method, the actual concrete floor slab bridge was measured from 33 m away and some internal defects were detected and visualized. Furthermore, a result for a railroad tunnel was compared with the Schmidt hammer rebound value and elastic wave velocity to verify the validity of the proposed method.

Bond characteristics of sprayed FRP composites bonded to concrete substrate considering various concrete surface conditions

This paper presents the results of pull-off bond tests carried out to investigate the bond characteristics of the sprayed FRP composites bonded to concrete substrate with various surface conditions. It was intended to evaluate the effect of key parameters considering field application conditions on the bond behavior and performance between the sprayed FRP layer and concrete surfaces. Key parameters used in this study consisted of the surface treatment method, saturation condition and the use of the primer coating. The results showed that the key parameters had significant effect on the bond behavior and performance of the sprayed FRP system bonded to concrete substrates being observed.

Runoff of pyrethroid insecticides from concrete surfaces following simulated and natural rainfalls

Intensive residential use of insecticides has resulted in their ubiquitous presence as contaminants in urban surface streams. For pest eradication, urban hard surfaces such as concrete are often directly treated with pesticides, and wind/water can also carry pesticides onto hard surfaces from surrounding areas. This study expanded on previous bench-scale studies by considering pesticide runoff caused by irrigation under dry weather conditions and rain during the wet season, and evaluated the effects of pesticide residence time on concrete, single versus recurring precipitations, precipitation intensity, and concrete surface conditions, on pesticide transferability to runoff water. Runoff from concrete 1 d after pesticide treatment contained high levels of bifenthrin (82 μg/L) and permethrin (5143 μg/L for cis and 5518 μg/L for trans), indicating the importance of preventing water contact on concrete after pesticide treatments. Although the runoff transferability quickly decreased as the pesticide residence time on concrete increased, detectable residues were still found in runoff water after 3 months (89 d) exposure to hot and dry summer conditions. ANOVA analysis showed that precipitation intensities and concrete surface conditions (i.e., acid wash, silicone seal, stamping, and addition of microsilica) did not significantly affect the pesticide transferability to runoff. For concrete slabs subjected to natural rainfalls during the winter wet season, pesticide levels in the runoff decreased as the time interval between pesticide application and the rain event increased. However, bifenthrin and permethrin were still detected at 0.15–0.17 and 0.75–1.15 μg/L in the rain runoff after 7 months (221 d) from the initial treatment. In addition, pesticide concentrations showed no decrease between the two rainfall events, suggesting that concrete surfaces contaminated by pesticides may act as a reservoir for pesticide residues, leading to sustained urban runoff contamination.