Surface Layer Of Concrete Research Articles

Assessment of the Influence of Features of Crack Formation in Reinforced Concrete Products on their Fire Resistance

The paper considers possible scenarios of cracking during heating and their impact on fire resistance using the example of a bending reinforced concrete structure (beam). It is shown that if the calculated critical temperature of reinforcement is less than the critical temperature of concrete (this indicates a significant load on the structure), then cracks in the tensile zone of concrete are formed after reaching the second stage of the stress-strain state. The concrete of the protective layer does not have time to degrade, the depth of the crack remains constant, and the fire resistance limit is calculated taking into account that the thickness of the protective layer of concrete is reduced by the depth of the crack opening. If the calculated critical temperature of the reinforcement is greater than the critical temperature of the concrete (this indicates a slight load on the structure), then cracks are formed as a result of the degradation of the surface layer of concrete. Their depth should constantly increase with the progression of the concrete layer heating to the critical temperature. In this case, the calculation of the fire resistance limit can be performed without taking into account the formation of cracks. Based on the considered assumptions, a methodology for assessing the impact of cracks on the fire resistance limit of bending reinforced concrete structures is proposed, which consists in analyzing the possibility of open cracks (which is facilitated by heating) and estimating their depth. At the next stage, the heating time of the concrete layer to the crack opening depth τΔ1 and the temperature in the crack after this time are estimated. Next, the time until the critical temperature of the reinforcement τΔ2 is estimated when the concrete layer is heated from the bottom of the crack to the reinforcement. The fire resistance limit is defined as the sum of τΔ1 and τΔ2. The results of the calculations according to the proposed methodology showed that the presence of open cracks in bending reinforced concrete structures can almost halve the fire resistance limit.

Evaluation of nanoparticle-enhanced silane and vinyl ester coatings for protecting concrete from ammonium sulfate

Inferior quality of concrete surface layers can lead to significant deterioration of concrete infrastructure due to the infiltration of fluids and deleterious substances from the surrounding environment. Concrete structures such as foundations, abutments, flatwork, and underground tanks in agricultural and mining zones, as well as slabs in factories producing ammonium-based fertilizers, are highly susceptible to ammonium sulfate attack, which is known as the most aggressive sulfate deterioration driven by acid-sulfate reactions. Coatings are an effective strategy for protecting such concrete structures to restore its performance and prolong its service life. Therefore, this study aimed at investigating the performance of nano-based coatings as superficial treatments for concrete elements exposed to aggravated exposures of ammonium sulfate. Silane (hydrophobic agent) and vinyl ester (membrane-forming polymer) were used as base resins, in which nano-clay and nano-calcium carbonate particulates were dispersed at different dosages (0, 2.5, and 5 %). In addition, a colloidal silica solution was used as a surface treatment. The durability of coated concrete specimens was evaluated under two ammonium sulfate exposures: full immersion and combined with cyclic environmental conditions (freezing-thawing and wetting-drying cycles). Degradation of concrete specimens was monitored by visual assessment and quantified in terms of mass and length changes over time. In addition, the deterioration mechanisms and coatings’ performance were studied by thermal, mineralogical, and microstructural tests. The results showed that colloidal silica could not adequately protect concrete specimens from these exposures. Conversely, silane nanocomposites improved the durability of concrete under both exposures and superior performance was generally observed for concrete specimens coated with vinyl ester nanocomposites.

Comparative analysis of selected machine learning techniques for predicting the pull-off strength of the surface layer of eco-friendly concrete

With recent trends reducing the carbon footprint of concrete, more novel materials are designed. It's mostly done by replacing cement with admixtures that are wastes in industrial processes. There is a need to provide reliable and accurate models to estimate the properties of the material. In this case the selected ML algorithms such as ANN, RF and DT were used for estimating the pull-off strength of the surface layer of cement mortar containing granite powder, fly ash and ground granulated blast furnace slag. The focus was on the cement-sand ratio of 1:3, replacing up to 30 % of the binder. Ultrasonic pulse velocity and pull-off strength of the surface layer. The analyses were performed in comparative manner and proved the accuracy of the designed models. The error values (MAPE, NRMSE and MAE) of the most effective model is below 3,5 %, indicating an extremely high success rate in prediction. An R2 ratio of 0.9436 confirms the very good fit of the model. Parametric tests were performed and SHAP analysis gave a better understanding of the models. The main conclusion of the study is to identify the possibility of replacing destructive testing with non-destructive testing supported by machine learning and material information to determine the pull-off strength of the subsurface layer at a selected depth for cement mortars containing waste materials. A particular advantage of the presented approach is the possibility of reducing the time to determine selected desired material parameters and the amount of testing required compared to the traditional approach.

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.

Impact of air exposure post-steam curing on the internal curing efficiency of porous ceramic roof-tile waste fine aggregate in steam-cured fly ash concrete

This study aims to elucidate the impact of drying on the internal curing effect of fine aggregates derived from roof-tile waste in steam-cured fly ash concrete. The research examines the compressive strength, mass loss, surface moisture content, and surface air permeability of the concrete under two conditions: conventional steam curing (followed by exposure to air) and six-day sealed curing post-steam curing. Additionally, pore size distributions were exclusively evaluated for concrete exposed to air post-steam curing. Results indicate that drying after steam curing negatively affects the internal curing by porous ceramic roof-tile waste. Nonetheless, internal curing effectively mitigated the negative impact of drying on the surface layer of steam-cured concrete.

Performance of concrete superficially treated with nano-modified coatings under sulfuric acid exposures

Protection of concrete surface layer is crucial for preserving serviceability and durability of concrete structures during their service life. Chemical attack by sulfuric acid is an aggressive exposure, commonly causing significant damage to concrete elements such as buildings' foundations and basement walls, buildings and structures affected by acid rain, industrial facilities, and wastewater treatment facilities. Hence, this study endeavored to evaluate the performance of nano-modified composites as surface treatments for concrete under severe chemical exposures. Nano-calcium carbonate and nano-clay particles were dispersed at different dosages (0, 2.5, and 5% by mass) in the neat coatings: vinyl ester (membrane-forming polymer) and silane (hydrophobic agent). Moreover, an amorphous colloidal silica (SiO2>50%) was also used as a superficial treatment for concrete. These coatings were applied to concrete specimens with water-to-binder ratios (w/b) of 0.40 (representing good quality/low penetrability concrete treated for prohibition of deterioration) and 0.60 (representing deteriorated/high penetrability concrete in need for rehabilitation). the wettability and initial transport characteristics of the coated concrete specimens were determined. In addition, the durability of superficially treated concrete specimens was examined under two aggressive exposures: full submergence in a 5% (by volume) sulfuric acid solution, and 5% sulfuric acid solution combined with wetting-drying cycles. During both exposures, the deterioration of concrete specimens was observed by visual inspection and quantified in terms of mass change. Furthermore, the damage mechanisms and coatings’ performance were studied by microstructural, mineralogical, and thermal analyses. The overall results showed that vinyl ester and vinyl ester nanocomposites significantly improved the durability of concrete specimens by an average of around 64% relative to that of the silane and silane nanocomposites; hence, they are recommended for field applications.

Experimental Study on Seismic Performance of Prefabricated Monolithic Concrete–Polystyrene Panel Composite Wall Panels

A normal composite wall panel is a structural component composed of polystyrene insulation boards and concrete surface layers reinforced with steel wire mesh. It can be entirely prefabricated in a factory or constructed with the concrete surface layers cast on-site. A novel prefabricated monolithic concrete–polystyrene panel composite wall panel (CPC wall panel) is proposed in this study. The CPC panel features a middle part that is prefabricated in the factory while the reinforced concrete regions at its two side ends are cast on-site. To evaluate the seismic performance of the wall panel, 18 CPC specimens were designed, manufactured, and quasi-statically tested, through which the structural behaviors, failure mode, and load-bearing capacity were studied. In addition, the influences of the height-to-width ratio and the vertical compressive stress level on the seismic performance of the CPC panels were also investigated. The test results showed that the connectors spaced at 400 mm × 500 mm could ensure the concrete layers on both sides of the polystyrene board worked collectively under seismic conditions. When subjected to lateral loads, the interface between the newly poured concrete and the existing concrete exhibited good bonding. Moreover, the failure mode of the CPC wall panel was largely correlated to the height-to-width ratio that, for specimens having four steel bars of 12 mm diameter and a height-to-width ratio greater than 1, the flexural failure was initially developed, followed by diagonal shear failure. In specimens with a height-to-width ratio of 1, flexural and diagonal shear failures occurred almost simultaneously. For specimens with a height-to-width ratio of less than 1, the final diagonal shear failure was predominant. The longitudinal reinforcing bars at the two ends of the CPC panels could effectively improve their lateral load-bearing capacity, with the enhancement influenced by the height-to-width ratio, the vertical load applied to the wall panel, and the cross-sectional area of the steel bars. In practice, the lateral load-bearing capacity of the CPC panel can be conservatively evaluated using the calculation method of the reinforced concrete shear walls. Finally, the ductility of the CPC specimens was affected by the height-to-width ratio and the axial compressive stress level, such that the specimens with a larger height-to-width ratio and lower axial compressive stress exhibited better ductility.

Study of Moulding Sands to Create Three-Layer Magnesium Concrete

Abstract The article is devoted to the problem of creating energy-efficient building materials for enclosing structures. The aim of the research is to develop a recipe and a method for moulding sands placing to create heat-insulating concrete of a multilayer structure. The three-layer magnesium concrete containing layers of different densities is an object of a scientific research. Compositions of moulding sands for concrete’s central and surface layers have been developed and studied. Materials specially developed were used as raw materials for moulding sands; they are as follows: composite magnesial binder and porous filler obtained by low-temperature firing of a granular mixture based on sodium liquid glass and thermal energy waste (fly ash from thermal power plants, aluminosilicate microsphere). Possibility of regulating moulding sand’s properties for concrete’s central layer by varying the content and fractional composition of porous granules has been shown. There has been proposed the moulding sand for surface layers of three-layer magnesium concrete containing crushed porous sand. The related composition of moulding sands favours with adhesion of concrete’s different layers. Various technological methods for producing magnesium concrete of a complex structure have been studied. The research reveals technological and operational characteristics of three-layer magnesium concrete obtained by horizontal and vertical deposition of moulding sands.

Viabilidade do concreto permeável como material delineado como sistema de detenção para áreas de segurança de pistas de aeroportos

Abstract From the late 1960’s airport engineers developed special paving material for arresting aircraft gears in event of overrun as a partial extension of a runway end safety area. Such pavement surface material, inverting a general concept, should be crushed over the first pass of gear wheels resulting the aircraft to sink and being promptly arrested resulting in abrupt loss of velocity, preferability avoiding loss of lives and injuries as well as with minimum risks for the airplane structural integrity. Herein is analyzed and discussed the possible application of pervious concrete for such a task by simulating an actual situation (Congonhas airport) and understanding the structural effects on the crushable concrete surface layer, pointing out stresses, deflections and required strengths for the material. Simulations regarded the critical aircraft A 320-200 as well as fire-fighters cars over the pavements. Analysis complied to Federal Aviation Administration requirements for non-standard pavement structures as well simulation of stresses trough the finite element method for medium-thickened plates. Compressive stresses along with flexural excessive stresses, besides predictable punching shear stresses allowed to conclude by the feasibility of using low strength pervious concrete as alternative for engineered material to be built as arresting system.

Оцінка впливу тріщин на вогнестійкість згинальних залізобетонних елементів

The paper considers possible scenarios of cracking during heating and their impact on fire resistance using the example of a bending reinforced concrete structure (beam). It is shown that if the calculated critical temperature of reinforcement is less than the critical temperature of concrete (this indicates a significant load on the structure), then cracks in the tensile zone of concrete are formed after reaching the second stage of the stress-strain state. The concrete of the protective layer does not have time to degrade, the depth of the crack remains constant, and the fire resistance limit is calculated taking into account that the thickness of the protective layer of concrete is reduced by the depth of the crack opening. If the calculated critical temperature of the reinforcement is greater than the critical temperature of the concrete (this indicates a slight load on the structure), then cracks are formed as a result of the degradation of the surface layer of concrete. Their depth should constantly increase with the progression of the concrete layer heating to the critical temperature. In this case, the calculation of the fire resistance limit can be performed without taking into account the formation of cracks. Based on the considered assumptions, a methodology for assessing the impact of cracks on the fire resistance limit of bending reinforced concrete structures is proposed, which consists in analyzing the possibility of open cracks (which is facilitated by heating) and estimating their depth. At the next stage, the heating time of the concrete layer to the crack opening depth τΔ1 and the temperature in the crack after this time are estimated. Next, the time until the critical temperature of the reinforcement τΔ2 is estimated when the concrete layer is heated from the bottom of the crack to the reinforcement. The fire resistance limit is defined as the sum of τΔ1 and τΔ2. The results of the calculations according to the proposed methodology showed that the presence of open cracks in bending reinforced concrete structures can almost halve the fire resistance limit.

Research on bond behavior of CFRP-concrete interface under quasi-static cyclic loading

In order to investigate the bond behavior of CFRP-concrete interface under quasi-static cyclic loading, static and quasi-static interface shear tests were conducted on three different adhesive layer thicknesses and two concrete strength grades. From these results, it can be seen that the load-slip envelope curves of the quasi-static cyclic loading specimen is similar to the quasi-static monotonic loading curves. As the adhesive thickness increases, the interface bearing capacity increases, the maximum strain of CFRP plate increases, and the effective bond length slightly increases. The interface failure mode is related to concrete strength. The failure mode of C30 concrete bonded with CFRP plate is cohesive failure of concrete surface layer, while the failure mode of C50 interface specimen is adhesive failure between CFRP and adhesive layer interface. As the thickness of the adhesive layer and the strength of the concrete increase, the interfacial bond strength and maximum strain of CFRP plate increase. It can be seen that the bond-slip envelope curves of the quasi-static cyclic loading specimen coincide well with the curves of the quasi-static monotonic loading specimen. As the magnitude of the cyclic loading increases, the unloading/reloading stiffness degradation, residual slip at zero load increases, and the dissipated energy increases. The fitting resulted in a degradation model of interfacial stiffness during quasi-static cyclic loading.

Design, implementation and performance prediction of profiled steel sheet-mixed aggregate recycled concrete hollow composite slab

Profiled steel sheet-mixed aggregate recycled concrete composite slabs are widely studied and applied in engineering applications by virtue of their good durability and recyclability. As an alternative to concrete composite slabs, concrete hollow composite slabs that can reduce their self-weight are also attracting people’s attention. However, the internal holes will increase the risk of collapse and shear failure of the concrete composite slabs. In order to reduce the risk and ensure the flexural performance of the concrete hollow composite slabs, this paper designs the recycled concrete hollow composite slabs with PVC pipes. A full-scale experiment is carried out on five open-mouth profiled steel sheet-mixed aggregate recycled concrete hollow composite slab specimens, to explore the influence of whether the bottom of the plate is reinforced, the thickness of the concrete surface layer and the hollow size on the working performance of the composite slabs. In order to predict the mechanical performance of the proposed hollow composite slabs, a prediction model based on artificial neural network (ANN) consisting of several sub-ANN modules is established. Moreover, according to the priority of the factors affecting the mechanical performance of composite slabs, a decision tree is designed to select appropriate testing sub-ANN module and thus improve the testing accuracy. Predicted results and experimental results are given to validate the feasibility and effectiveness of the developed ANN-based prediction framework for the mechanical performance prediction of composite slabs.

Investigation of 6PPD-Quinone in Rubberized Asphalt Concrete Mixtures.

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD)-quinone (6PPD-Q), a transformation byproduct of 6PPD used in tires as an antiozonant and antioxidant, was recently discovered as the chemical primarily responsible for the acute lethal toxicity of urban storm runoff to coho salmon. The asphalt concrete (AC) surface layer is the primary medium to contact 6PPD-Q immediately upon its release from tires, and the addition of recycled tire rubber (RTR) to the asphalt binder and mixture is a widely accepted practice in asphalt production. Therefore, it is urgent to understand the fate of 6PPD-Q at the asphalt concrete surface layer-water interface. This study analyzed the sorption and desorption of 6PPD-Q by compacted and crushed loose (loose particles, ∼5 mm) rubberized asphalt mixtures and their mobilization from compacted asphalt mixtures during simulated rainfall events. It should be noted that the crushed loose asphalt mixtures demonstrated the physicochemical properties of the asphalt materials, while the compacted asphalt mixtures represent in-service AC layers. Sorption of 6PPD-Q by crushed loose and compacted asphalt mixtures reached equilibrium within 12 days, with a sorption coefficient of 151.57-257.51 L/kg for compacted asphalt mixtures. Within 12 days, desorption of 6PPD-Q from crushed loose and compacted rubberized asphalt mixtures (20 g particles/L) to the double deionized (DDI) water and synthetic stormwater was 0.01-0.09 and 0.025-0.05 μg/L, respectively. Through the rainfall simulation experiments, 0.0015-0.0049 μg/L 6PPD-Q was detected in the runoff water, much lower than the lethal concentration (LC50) of 6PPD-Q of 0.095 μg/L and 308.67 μg/L for coho salmon and zebrafish larvae. Our results indicate that, while the release of 6PPD-Q from compacted rubberized asphalt mixtures is minor, the mixtures can serve as sorbents for tire-derived 6PPD-Q and retain this emerging contaminant.

Shaking table tests on 0.5-scale multistory models of plate-type modular steel and composite buildings with semi-rigid corner connections

To study the dynamic properties and seismic response of global plate-type modular steel and composite structures with semi-rigid corner connections, shaking table tests were conducted on three 0.5-scale multistory plate-type modular models. This paper presents the testing program and results, including the dynamic characteristics and earthquake performance. Under the excitation of seismic loads, the bolts connected to the corners were easily loosened, the gaps between the composite wall plates increased, and the concrete surface layer of doorways and windows was damaged and fell off. The test results showed that as the peak ground acceleration increased, the fundamental frequency decreased, the damping ratio increased, and the acceleration amplification factor decreased. The initial lateral stiffness of plate-type modular composite structures with wall panels was eight to nine times that of plate-type steel frame structures owing to the strong skin effect of the wall panels. The stiffness of complete composite structures decreased by approximately 50% under a nine-degree rare seismic intensity owing to the deterioration of the bolt rotation stiffness and damage to the wall panel. The maximum interstory drifts of the complete plate-type modular building under rare earthquakes were small, which meets the requirements of the seismic design code.

Temporal and spatial temperature predictions for flexible pavement layers using numerical thermal analysis and verified with large datasets

The pavement temperature patterns play a significant role in the performance of flexible pavements containing asphalt concrete surface layers for several reasons. Since asphalt concrete behaves as a viscoelastic material at medium to high service temperatures, the structural response of the pavement is affected by the temperature history and the magnitude and duration of the wheel loads applied on the pavement. Therefore, predicting the pavement temperature patterns in a scalable manner (i.e., daily, seasonal, annual) is vital for a more accurate simulation of pavement response and performance, particularly the permanent deformation (rutting). This can result in more effective pavement designs. A numerical model was developed in this paper to predict the temperatures in asphalt layers by using the heat transfer theory and the Finite Element method with the help of proprietary software. A model that can predict the pavement temperatures continuously for one year covering all four seasons at time intervals that allow pavement distress prediction for each axle load cycle and calibrated with high-quality measured data is the main contribution of this study. Among the parameters that significantly affect pavement temperature prediction, the convective heat transfer at the air-pavement interface is of utmost importance. Therefore, the Convection Heat Transfer Coefficient (CHTC) for the air-pavement interface was also selected as an exploratory focus area for this paper. Two approaches were used to estimate the CHTC needed for the heat-transfer model. An error analysis was conducted to assess the accuracy of the pavement temperature prediction by using a large, measured dataset from a field test. The error of temperature predictions for the whole year was found to be minimum when the value of CHTC was equal to 21 W/(m2K). The error observed in winter predictions with the wind speed model of CHTC was minimized when a constant value of 60 W/(m2K) was used for CHTC. The significance of the convective heat transfer component in the FE model was identified through the improvements obtained by adapting the value of CHTC. Correlation analysis also identified a connection between the prediction error and relative humidity. Further research is underway to improve the temperature prediction model using additional parameters (i.e., relative humidity, cloud cover) and more refined data analytics approaches.

Noise mapping and acoustic evaluation of different pavements in the city of Fortaleza, northeast Brazil.

The Climate Action Plan developed by the Brazilian city of Fortaleza has encouraged active mobility aiming pedestrians' prioritization, thermal and drainage benefits, which has led to replacement of Asphalt Concrete (AC) surface layers by Interlocking Concrete Pavers (ICP) and Porous Friction Course (PFC). This work aims to evaluate the impact of these infrastructure changes on environmental noise levels. As a case study, 25 measurements on an urban avenue were made in 6 road sections with AC, ICP and PFC pavement surfaces. It was modeled in CADNA-A software and some scenarios with different traffic conditions were compared. The results showed that the use of PFC led to a noise attenuation of 3 dB(A) in LAeq when compared to AC. A reduction in the maximum speed limit from 60 kmph to 50 kmph led to a noise attenuation of 1.2 dB(A). In the section with ICP, measured data showed reduction in speed and traffic flow when compared to other pavements. Thus, despite the higher tire/road noise caused by the ICP, its application on urban roads led to a similar LAeq. The authors conclude that the application of these alternative pavements, when accompanied by traffic calming strategies, can reduce road traffic noise.

Evaluation of Moisture Transport Properties Based on Modelling of Silane-based Impregnation Agent Effects on Concrete Surface Layer

It is now desirable to establish a technique for long-term prediction of the effects of silane-based impregnation agent on concrete structures exposed to various environments. To meet this requirement, the purpose of this study is set to establish the model to evaluate the effect of a silane-based impregnation agent on the waterproofing properties of cementitious materials based on microscopic mechanisms. Several mortar specimens were prepared with the silane-based impregnation agent, and moisture absorption and evaporation experiments were conducted. The results showed that the application of the agent was shown to effectively inhibit the penetration of moisture into the interior of the cementitious materials. The effect of the silane-based impregnation agent was modeled in a multiscale pore structure model by applying a microscopic water-repellent effect to the pores in which no pore water was present at the time of agent coating. The analysis with proposed model showed that, as in the experiment, the moisture supply was reduced by the application of the agent, whereas the amount of moisture loss remained almost the same with and without the agent. Moreover, the analysis quantitatively showed that the water content can continue to decrease with silane treatments, even under repeated wet-dry conditions.

Investigation of the Deterioration of Medium-Rise-Wall Type Reinforced Concrete Buildings with External Insulation in Snowy Cold Districts

We have clarified that external insulation reduces the probability of reinforcement corrosion in reinforced concrete buildings in cold snowy districts by 45–78%. Renovation of external insulation is one of the effective methods for improving the insulation performance and durability of reinforced concrete buildings, but there are almost no data that demonstrate durability. Therefore, the carbonation depth and the cover depth were investigated for six medium-rise-wall type reinforced concrete buildings in Hokkaido, Japan, which had been refurbished for external insulation. As a result, it was clarified that the external insulation suppressed the carbonation depth by 30% or more, even when the bonding method of the external insulation was different. In addition, it was clarified that the external insulation further suppressed carbonation in walls where the carbonation depth tended to increase in snowy cold districts. Specifically, external insulation reduced carbonation by up to 35% on surfaces that tend to dry out due to sunlight, and by 49% on surfaces that are affected by water that deteriorates the concrete surface layer.

Experimental Comparison of Efficiency of Water-Soluble and Solvent Hydrophobic Agents for Concrete

The paper presents the results and assessment of the properties and capabilities of new types of surface hydrophobic agents for the treatment of fresh and matured surfaces of concrete and other cement-bound layers. Hydrophobisation prevents the premature evaporation of water and thus plastic shrinkage, which inevitably leads to the formation of cracks in cement-based structures. The influence of the new type of hydrophobic agents, epoxy water-based (EWH) and acrylate (AH) containing solvent, on the physical and mechanical properties of the treated concrete samples was assessed, including the adhesion of hydrophobisation on the concrete surface layers. It was confirmed that surface hydrophobisation successfully prevents premature evaporation of water, and thus, plastic shrinkage (concrete treated with EWH_0.3 showed more than two times lower shrinkage than reference concrete). The concrete samples treated by hydrophobisation agents showed higher strength after 120 days (37.5 MPa) in comparison with untreated concrete (32.8 MPa). Different properties were recorded with different types of hydrophobisation agents, including compressive strength after 90 days (31.2 MPa with EWH_0.15, and 35.9 MPa with AH_0.15). Water absorption after 120 days was lowest with EWH_0.3 samples (3.77%), two times lower than AH_0.15 (6.98%). The layer of hydrophobisation agent EWH_0.3 was thicker than AH_0.15, leading to lower water absorption of treated concrete and higher resistance to defrosting chemicals—waste 8.5. g/m2 with EWH_0.3 in comparison to 35.7 g/m2 with AH_0.15. Furthermore, a difference in the hydrophobisation behaviour was shown with blocking of infiltration from the chemically aggressive environment into the concrete substrate. Deterioration of the surface concrete exposed to 10% HCl solution was worse with AH_0.15; but the concrete surface treated with AH_0.15 showed better resistance than the EWH treated surface, when exposed to 5% CH3COOH. Degradation of the hydrophobisation integrity and the loss of cohesion between the concrete and the surface treatment after exposure to acetic acid and hydrochloric acid was observed using scanning electron microscopy (SEM).

Influence analysis of the selection of foundation model on fatigue stress evaluation results of cement concrete pavement-based on GPR and FWD

• The internal structural condition of the pavement was analyzed by FWD and GPR. • The applicability of different foundation models to cement pavement was analyzed. • The specific influence of h c , E c , E t on load and temperature stress was analyzed. This study showed a method of selecting appropriate foundation models for fatigue stress analysis of cement concrete pavement. Based on the strength and damage conditions of the base and the correlation between the crack rate of the base ( C b ) and modulus of the base ( E t ), the integrity and stiffness of the base were evaluated. Moreover, the applicability of the base to the Winkler foundation model and the elastic half-space foundation model for each road section was clarified based on the evaluation results. The cement concrete pavement's load stresses and temperature stresses under different technical conditions were calculated by combining the parameters of the thickness of the cement concrete surface layer ( h c ), modulus of the cement concrete surface layer ( E c ), and E t of each road section and the compatible foundation models. The effects of the changes of parameters h c , E c , and E t on the load and temperature stresses of cement concrete surface layers under different foundation models were also investigated. It was observed that the effects of E c and E t on the temperature stresses of the cement concrete surface layer are more pronounced compared to h c . h c is the parameter that has the most significant influence on the internal load stress of the cement concrete surface layer. The Winkler foundation model is more sensitive to the change in h c , and the Elastic half-space foundation model is more sensitive to the change of E c and E t . No matter what kind of technical condition the pavement is and what type of foundation model is adopted, the influence degree of each structural parameter on the load stress of the cement concrete surface layer is not different obviously, and the influence ratio is relatively stable. However, for the temperature stress, under different pavement technical conditions, the changing amplitude of temperature stress caused by the changes of h c , E c , and E t is significantly different, and the greater the h c is, the greater the influence of the changes of h c , E c , and E t on the temperature stress is.