Surface Layer Of Concrete Research Articles

Detection of the synergetic influence of chemical and microbiological factors on the properties of concrete constructions at chemical plants during the long-term service

Long-term operation of reinforced concrete structures in the conditions of chemical enterprises has a powerful negative impact on the physical and chemical properties of concrete, which leads to its destruction. The aim of this research is to determine the effect of biological and chemical corrosion on concrete structures in the workshop for the production of titanium dioxide by the sulphate method and the storage of finished products. In particular, chemical production for the synthesis of titanium dioxide by the sulfate method causes the rapid course of chemical (acid and sulfate) and microbiological (thionic bacteria and microscopic fungi) corrosion processes. These corrosion processes reinforce each other according to a synergistic principle. As a result, temperature-programmed desorption mass spectrometry (TPD MS) and scanning electron microscopy have experimentally proven the presence and spatial localization of colonies of thionic bacteria and microscopic fungi in concrete structures. Correlations between the intensity of biochemical corrosion and the depth of damage to the microstructures of concrete structures have been established. Moreover, a change in the chemical composition of concrete in the workshop for the production of titanium dioxide (increased SO2 content and reduced CO2) and the formation of gypsum crystals (CaSO4 2H2O) as a result of the dissimilation of microorganisms was established. Also, in the storage room for finished products, calcium citrate crystals and a violation of the formation of calcium carbonate are formed in the surface layers of concrete. In addition, the results of the study can be used to develop antimicrobial and anticorrosive protective agents to stop the biochemical corrosion of concrete in a chemical plant

Engineering Disaster Investigation and Recurrence of the Covering Effect in a Petroleum and Gas Station in Seasonally Frozen Soil Region

The impermeable engineering surface layer in the cold regions blocks the water and heat exchange between the foundation soil and the atmospheric environment. Especially in cold areas with significant temperature differences, the moisture in the foundation soil accumulates at the bottom of the structure layer to form a covering effect. This will exacerbate the occurrence of engineering freeze-thaw diseases. This paper conducts a disease survey of the Guanshan oil and gas station site, which is located in a seasonally frozen soil zone. The ponding and freeze-thaw diseases under the concrete cover are analyzed. The formation process of the pot covering effect in the lower part of the concrete surface layer was reproduced through indoor tests. In addition, a water-vapor-heat coupling model of unsaturated soil was established, which quantitatively produced the formation process of silty clay covering under the concrete slab. The results show that (1) in-situ monitoring demonstrated that the water content of the roadbed soil from 0 to 50 cm below the concrete slab gathered significantly, with the water content increasing by 5 to 30%. (2) Under the action of the indoor time-varying covering effect, the moisture content of silty clay will increase with the number of freezing-thawing cycles, with a maximum migration amount of 6%. (3) Seasonal temperature changes lead to the accumulation of water in the subgrade surface, and the maximum accumulation amount is 32%. (4) During the freezing period, the liquid water and vapor water in the subgrade migrate to the surface layer of the subgrade. As a result, the moisture content of the subgrade surface layer increases, while the melting period is the opposite. The above research results can provide theoretical support and scientific countermeasures for engineering design and disease control in cold regions.

A comparison between uniform and galvanic corrosion rate in carbonation induced corrosion of reinforced concrete

Carbonation-induced corrosion is usually considered in uniform or generalized corrosion. This is true for small laboratory samples but not necessary the case for real reinforced concrete structures built with multilayers reinforcement. Multi-layers reinforcement could lead to a galvanic corrosion between first de-passivated layer closed to the concrete surface and deeper layers still passivated. The present paper compares the uniform corrosion density and the galvanic corrosion density for concrete samples made with two different type of cements. CEM III cement despite their higher susceptibility to carbonation show a significant lower galvanic corrosion density, which would lead to a significant increase in the service life of RC structures, exposed to carbonation.

INVESTIGATION OF THE OPERATING MODE OF THE DYNAMIC SYSTEM "VIBRATION PLATE - POLYMER CONCRETE" WITH SURFACE COMPACTION

For the theoretical definition of the law of motion and operating modes of the vibration plate of the surface vibration working body with polymer concrete, a study of the dynamic system "vibration plate - polymer concrete" was carried out. In this dynamic system, compacted polymer concrete is presented in the form of a system with distributed parameters, which takes into account the action of elastic and dissipative resistance forces acting on the part of polymer concrete when it is deformed into a form on a rigid foundation. According to the accepted rheological model of polymer concrete for conditions of uniaxial stress state, a partial derivative relationship is proposed between the stress and deformation of polymer concrete, the nature of which depends on the dynamic modulus of elastic deformation, the dynamic modulus of elastic deformation of Maxwell and the coefficient of dynamic viscosity. A wave equation of vibrations has been compiled, which describes the propagation of elastic-viscous deformation waves in polymer concrete, which is deformed by a surface vibrating working body, the solutions of which made it possible to determine: the regularity of propagation of elastic-viscous deformation waves in compacted polymer concrete, as well as theoretical expressions for the numerical determination of the reduced coefficients stiffness and dissipative resistance of polymer concrete, added mass; the law of motion and the amplitude of vibrations of the vibrating plate, as well as the laws of motion of the surface layer of polymer concrete. The obtained theoretical dependences make it possible to reasonably determine the rational parameters of the vibrating working body and the main operating modes of the vibrating plate, depending on the found physical and mechanical characteristics of the polymer concrete compacted by vibration. The results obtained can be further used to carry out theoretical studies on the analytical determination of the nature of the change in stresses along the height of the compacted layer of polymer concrete, as well as in the analysis and synthesis of the obtained vibro-shock mode of operation of the vibrating plate.

Effect of limestone powder and fly ash on the pH evolution coefficient of concrete in a sulfate-freeze–thaw environment

Limestone powder has been widely used in concrete during fly ash shortages and in the green and sustainable development of concrete materials. Because the effect of limestone powder on concrete alkalinity is not well understood, we research the effect of 10% limestone powder concrete, 10% fly ash concrete, and pure cement concrete at different depths on the pH value of the initial state, microstructure and compressive strength, sulfate immersion, and number of sulfate–freeze–thaw cycles at different pH value coefficients of concrete erosion products formed in a sulfate-freeze–thaw environment. Limestone powder has no obvious effect on the pH value of concrete in the initial state, while fly ash reduces the pH value of concrete in the initial state. In the sulfate-freeze–thaw environment, the protective property of limestone powder concrete is slightly stronger than that of pure cement concrete, and the protective property of fly ash concrete is weaker than that of pure cement concrete. The effect of sulfate immersion and the sulfate-freeze–thaw environment on the pH value of the concrete surface layer is greater, which is confirmed by the results of synchronous thermal analysis. TSA (the thaumasite form of sulfate attack)-type damage to limestone powder concrete occurred in the sulfate-freeze–thaw environment, and the C–S–H gel content in 10% limestone powder concrete was significantly less than that in 10% fly ash concrete and pure cement concrete at depths of 0–5 mm, 5–10 mm and 10–15 mm, which reduced the content of C–S–H gel.

Performance evaluation of pervious concrete pavements with recycled concrete aggregate

The construction and demolition waste (CDW) production and soil sealing are some of the main problems associated with urbanization. The use of pervious concrete pavements with recycled aggregates appears as an innovative and sustainable solution in both environmental and economic aspects. This work evaluates the behavior of pervious concrete produced with CDW aggregates. In order to better control the composition and to achieve better mechanical behavior, CDW composed only by recycled concrete was employed. The performance of the pervious concrete produced with different replacement levels of natural aggregates (NA) by recycled concrete aggregate (RCA), the influence of the rheology modifying admixture use, and the water-cement ratio reduction were investigated. Porosity, hardened density, hydraulic conductivity, infiltration, compressive and flexural tensile strengths, abrasion resistance, elasticity modulus, and Poisson's ratio were analyzed. The laboratory study results showed that the RCA replacement improves the hydraulic properties and decrease mechanical behavior. A test section composed of a pervious concrete surface layer with 100% RCA was built to verify the field performance. In situ infiltration tests were performed, and a Light Weight Deflectometer (LWD) was used to measure pavement deflections. Comparing the field results to those obtained in laboratory, it was found that only the compressive strength showed significant difference. The high standard deviation in test results strengthens the need for strict control of the material physical properties in the field. The global analysis of laboratory and field results showed that the sustainable concrete developed follows the Brazilian standard for pervious pavements and international recommendations.

Influence of the dry/wet ratio on the chloride convection zone of concrete in a marine environment

A convection zone appears in chloride content analysis in the concrete surface layer of when it is subjected to long-term to the marine atmosphere and tidal zones. To reveal the influence of the corrosion environment and concrete materials on the peak chloride concentration Cmax and convection zone depth Δx, this paper studies the evolution of the convection zone of concrete in long-term field experiments in a marine tidal zone and indoor experiments based on simulated drying-wetting cycles. Concrete includes Portland cement concrete and high-performance concrete containing ground granulated blast furnace slag (GGBS) and fly ash. Results indicate that greater the dry/wet ratio is, the earlier the onset of the convection zone is. Both the Cmax and Δx increase with the dry/wet ratio. The Cmax and Δx follows a power function with exposure time. Additionally, concrete containing GGBS and fly ash can significantly decrease Cmax, but cannot retard convection zone development in marine tidal environment compared with Portland cement concrete.

Salt frost attack on concrete: the combined effect of cryogenic suction and chloride binding on ice formation

Scaling of concrete due to salt frost attack is an important durability issue in moderate and cold climates. The actual damage mechanism is still not completely understood. Two recent damage theories—the glue spall theory and the cryogenic suction theory—offer plausible, but conflicting explanations for the salt frost scaling mechanism. The present study deals with the cryogenic suction theory, which assumes that freezing concrete can take up unfrozen brine from a partly frozen deicing solution during salt frost attack. According to the model hypothesis, the resulting saturation of the concrete surface layer intensifies the ice formation in this layer and causes salt frost scaling. In this study an experimental technique was developed that makes it possible to quantify to which extent brine uptake can increase ice formation in hardened cement paste (used as a model material for concrete). The experiments were carried out with low temperature differential scanning calorimetry, where specimens were subjected to freeze–thaw cycles while being in contact with NaCl brine. Results showed that the ice content in the specimens increased with subsequent freeze–thaw cycles due to the brine uptake at temperatures below 0 °C. The ability of the hardened cement paste to bind chlorides from the absorbed brine at the same time affected the freezing/melting behavior of the pore solution and the magnitude of the ice content.

A new method for hydraulic mass concrete temperature control: Design and experiment

In this paper, a new method for hydraulic mass concrete temperature control to reduce temperature stress is proposed. Based on dam temperature distribution characteristics, an external heating and cooling source is used to make the water circulate in the pre-embedded pipe net in the concrete surface layer to control the concrete temperature. The minimum adverse strain principle is used to design the key parameters of the control system, and the strain caused by temperature and moisture is considered because of the porousness of concrete. The feasibility of the new method is studied via a mass concrete (1 m × 1 m × 1 m) experiment with pre-embedded temperature and moisture sensors under cold environmental conditions. The temperature and moisture evolutions in the control process show that the concrete temperature can be effectively controlled by the new method, but temperature control also has a great effect on the moisture in the surface layer concrete. Considering that the decreasing moisture of surface layer concrete in the temperature control process can also lead to adverse strain, based on the coupled heat and moisture transfer theory, the key parameters of the control system in the experiment are studied and optimized via simulations to reduce adverse strain.

Temperature and Strain Monitoring Analysis of Self-Compacting Concrete Bridge Decks with Mechanized Sand

The temperature control of self-compacting concrete with machine-made sand is an important research element related to the safety of actual projects. A reasonable and feasible temperature and strain monitoring scheme was designed for the bridge abutment project of Honghezhou Special Bridge in Yunnan Province, and the monitoring results of the concrete abutment on site were analyzed. The results show that the temperature of self-compacting concrete with mechanism sand has the characteristics of large temperature rise and rapid cooling compared with ordinary concrete, and the concrete surface layer is prone to cracking from 1.5d to 4d of age, and the concrete foundation part is prone to cracking at about 9d of age. It can provide reference for the temperature crack prevention and control of similar mechanism sand self-compacting concrete projects.

Project Scheduling Analysis Using the Precedence Diagram Method (PDM) Case Study: Surabaya’s City Outer East Ring Road Construction Project (Segment 1)

The project acceleration by the Crash Program is one of the ways that is often used to make time and cost efficiency on an ongoing project. Acceleration of project completion time will affect the efficiency of equipment and labor productivity. In the case study of the Surabaya Outer East Ring Road Project Construction Segment 1, a project that has the potential to be accelerated is discussed in order to obtain efficiency values in terms of time and cost, Project acceleration by means of the Crash Program using the Precedence Diagram Method (PDM) method to determine the value of efficiency. This project uses resources, in this research the software used is Microsoft Project 2016. The research method used is to design network planning, find the critical path for each job, determine the work that has the potential to be accelerated, calculate the crash cost in additional working hours. and work shifts, calculating direct costs and indirect costs for each activity that changes due to changes in the duration of implementation, calculating the cost slope. Application of the Crash Program in the work of Asphalt Concrete Surface Layers (AC) thick 5 cm in the project will have an impact on increasing the time efficiency previously planned from 180 working days to 175 working days and efficiency with the difference in project costs of Rp. 18.313.935,8 with a ratio of 0,997 between the PDM method compared to the cost of the contract value calculated using the crashing project method.

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.

The Mechanical Analysis of Cement Concrete Surface Layer With Load - transfer Bar for Joints Based on Computer

To establish a joint dowel bar and dowel bar set of cement concrete pavement structure in three dimensional finite element model, using the method of numerical analysis, analysis of the joint of cement concrete road surface of the load stress, deflection and deflection difference, to study the foundation modulus, dowel bar diameter on the load stress and the influence law of deflection is poor, and the condition of the same calculation results are analyzed in comparison. The results show that the principal stress, shear stress, deflection value and deflection difference decrease with the increase of the diameter of the rod. When the diameter of the transmission rod is greater than 35mm, the effect of increasing the diameter of the transmission rod on reducing the stress value at the calculated point in the cement concrete surface layer is not obvious. The calculated point load stress and deflection difference of cement concrete surface layer are obviously less than the calculated results when no load rod is installed in joints. When the foundation modulus is not greater than 800MPa, it is suggested to estimate the joint load transfer efficiency based on shear stress: when the foundation modulus is greater than 800MPa, it is suggested to estimate the joint load transfer efficiency based on the bending and sinking value or the principal stress[1-2].

Investigation of the technological factors‘ influence on the formation of the repair compositions‘ properties

Power transmission lines (PTL) belong to strategic facilities, on the reliability of which the life support of the country depends. Most of the currently operated PTLs were put into operation in the twentieth century, and now there is a problem of assessing their technical condition, repairing, if necessary, and maintaining them in working order. The defects appeared during the operation of PTL reinforced concrete elements have different localization and manifestation degree, but destruction of the concrete surface layer with reinforcement exposure is a characteristic, more often at the base of the PTL frame. The aim of the work is to select the optimal composition of the repair mortar based on non-shrinking and expanding cements, ensuring reliable adhesion of the repair mortar to the concrete of the structure, which will allow restoring the bearing and operational characteristics in the repaired PTL reinforced concrete elements at the design level.

Highly-efficient green photocatalytic cementitious materials with robust weathering resistance: From laboratory to application.

The combined use of nano-TiO2 with cementitious materials offers an environmentally-friendly way to combat the air pollution problem. However, a trade-off between a high efficiency and a robust weathering resistance has often to be made for most of the attempted nano-TiO2 incorporation methods. This paper developed a simple and effective "spraying" method to coat nano-TiO2 particles on the surface of concrete surface layers (CSL). The results showed that the NOx removal rate of the samples increased with an increase in both the concentrations of nano-TiO2 solutions and the number of times of the spraying action. And the conditions for preparation of the Spray AB (the CSL were first sprayed with the 30gL-1 TiO2-solution 20 times, followed by mechanical compaction, and for another 20 times after the compaction) were found to be optimal in terms of NOx removal performance and weathering resistance. The Spray AB was superior to the 5% TiO2-intermixed samples with respect to photocatalytic NOx removal ability. Compared with TiO2-dip-coated samples, the Spray AB samples had better and robust weathering resistance. A case study on the factory-fabricated green Eco-blocks (produced by the laboratory-developed spray method and the conventional intermix method) was performed. Examination and comparison on their respective photocatalytic NOx removal further verified the advantages of the spray method over the intermix method.

Corrosion resistance of concrete strengthened with fibre-reinforced polymer sheets

The corrosion resistance of concrete strengthened with three types of fibre-reinforced polymer (FRP) sheets (unidirectional carbon-FRP (CFRP), unidirectional basalt-FRP (BFRP) and bidirectional BFRP) was evaluated under chloride attack and the combined attack of chloride and ultraviolet radiation. After different corrosion durations, powder samples were collected from various depths of the concrete specimens to measure the total chloride ion concentrations (CICs). Scanning electron microscopy (SEM) was conducted to analyse the microscale morphology changes of the concrete surface layer, FRP fibre layer and resin matrix layer before and after combined attack. The results showed that all three types of FRP sheet provided significant chloride ion resistance, with the barrier effect of CFRP being better than that of BFRP under the same conditions. The total CIC of the FRP-strengthened concretes was higher under the combined attack than under chloride attack alone. The SEM observations showed that the resin matrix and fibre filaments of the FRP layer under combined attack were damaged, resulting in an increase in the permeability of the FRP-strengthened concretes. Finally, a time-varying model of CIC inside the FRP-strengthened concrete under chloride attack was established.

The Numerical study of the influence of a two-scale pore structure on the dynamic strength of water-saturated concrete

Many infrastructural concrete facilities, such as dams, bridge footings, foundations of port facilities and offshore drilling platforms, operate in a permanent contact with water. The permeable fractured-porous structure of concrete determines the water-saturated state of the surface layers of such concrete elements. Under dynamic contact loading, the pore fluid is capable of exerting a significant mechanical influence on the local stress-strain state and strength characteristics of the surface layers of concrete. This has to be taken into account when assessing the wear intensity of surface layers and predicting a concrete element’s service life. The aforesaid determines the relevance of the study aimed at identifying the influence of the pore fluid and characteristics of the concrete pore structure on the strength and fracture pattern under quasistatic and dynamic compressive loading. The present work is devoted to the theoretical study and generalization of the laws of mechanical influence of the pore fluid on the dynamic strength of high-strength concrete with a two-scale pore structure. The emphasis in the study is on analyzing the contributions of each of the pore subsystems to the integral mechanical effect of the fluid. To carry out such an analysis, a coupled hydromechanical model is developed. It takes into account the compositional structure of concrete, the presence of a pore space in a cement stone of two different scales, the interaction of a pore liquid and a solid-phase skeleton based on the Bio poroelasticity model, as well as fluid filtration in a pore space. By using the developed model were performed the numerical studies of the dependence between the compressive strength of the representative concrete volumes of the mesoscopic scale on the strain rate, the sample size, the pore fluid viscosity, and pore structure parameters. The simulation results showed the possibility of combining the obtained dependencies into a generalized (master) curve in terms of a combined dimensionless parameter, which has the meaning similar to the Darcy number. We identified two key factors that control the type and parameters of the concrete master curve of the dynamic strength. The first factor is the mobility of the pore fluid in the network of the capillary pores. It determines the rate of stress equalization in the porous skeleton due to fluid flow. The second factor is the interconnection of large micropores with the network of the small capillary pore channels. It determines the magnitude of the decrease in stress concentration in micropores by filtering the excess pore fluid into the capillary pore network. It is shown that the contributions of these two factors to the amplitude of variation of the dynamic strength of the water-saturated concrete are additive, and their total contribution reaches 25 %.

Development of Microwave Slow-Wave Comb Applicators for Soil Treatment at Frequencies 2.45 and 0.922 GHz (Theory, Design, and Experimental Study)

In agriculture and industry, it is often necessary to heat surface layers of material like soil, timber, concrete, and so on, with microwave (MW) energy. Traditional MW irradiators (antennas) cannot restrain their heating to the surface, with the energy penetrating deeply into the material. Slow-wave comb applicators can provide the required energy distribution in the surface layer. Theoretical analyses of the comb applicators used for heating were carried out and on this basis, three comb applicators were designed and made for soil treatment: two applicators Comb 1 and Comb 2 for frequency 2.45 GHz and Comb 3 for frequency 0.922 GHz. An experimental study of applicators was carried out using two MW plants: 30 kW (2.45 GHz) and 60 kW (0.922 GHz) for heating soil with moisture content in the range from 32% to 173% and density 460 to 1290 kg m−3. The study showed that comb applicators provide the following advantages: reduction in energy dissipation in material depth and release of the significant part of applied MW energy in layers close to the applicator surface. Comb applicators can provide the required soil top layer treatment (sterilization) with reasonable efficiency and can be recommended for practical use in shallow soil treatment for weed seed and pathogen control in agricultural applications. Comb applicators can also be used for effective heating and MW treatment of the surface layers of wood, concrete, bricks, plastics, and other dielectric materials.

Havaalanı Kaplamalarını Asfalt ve Beton ile Yeniden Kaplamanın Karşılaştırmalı Dizayn ve Ekonomik Analizi

Overlays for airfield pavements are one of the cost effective and efficient pavement rehabilitation options. In this study, the Federal Aviation Administration’s state-of-the-art mechanistic-empirical overlay design methodology (FAARFIELD) was explained, design examples using FAARFIELD version 1.42. for both concrete and asphalt overlays were presented, and the results of these examples were compared. For the overlay design scenarios on existing asphalt surface layers, it was found that, overlay thickness decreases, as existing asphalt surface layer thickness increases, and calculated concrete overlay thicknesses were higher than calculated asphalt overlay thicknesses for the same existing asphalt surface layer thicknesses. On the other hand, for the overlay design scenarios on existing concrete surface layers, both asphalt and concrete overlay thicknesses were found to be very similar to each other. Based on FAARFIELD-calculated overlay thicknesses, an economic analysis was carried out to find out the most economic overlay design options for a variety of design scenarios. Although for some overlay cases concrete overlay design thicknesses were found to be higher than asphalt overlay design thickness, cost of concrete overlays was found to be less than that of asphalt overlays. This is because unit cost for concrete materials is less than that for asphalt materials. Incorporating a state-of-the-art mechanistic-empirical overlay design for airfield overlay pavements as well as considering local cost in the economic analysis to determine which type of overlay would be a more suitable option for a variety of pavement design cases would be very beneficial to Turkish airfield pavement design practices.

Durability of Concrete Superficially Treated with Nano-Silica and Silane/Nano-Clay Coatings

Protection of the surface layer of concrete is essential for achieving durability and functionality of concrete elements during their service life. In this paper, an effort is made to utilize colloidal nano-silica (5%–50%) and a synthesized nanocomposite as superficial treatments for concrete; silane was used as the neat resin to disperse nano-montmorillonite particles at different dosages (5% and 10%). The coatings were applied to a typical concrete mixture used for residential concrete in North America. The transport properties of the treated concrete were characterized using the rapid chloride penetrability test and the absorption/desorption percentages. Moreover, concrete was evaluated under severe durability exposure involving physical salt attack (PSA), which is a wetting/drying regime responsible for surface damage of concrete elements subjected to continuous salt supply along with cyclic ambient conditions. Deterioration was visually assessed and quantified using mass change. In addition, thermal and microscopy analyses were performed on concrete specimens to elucidate the mechanisms of enhancement by surface treatment. The results showed that increasing the concentration of nano-silica particles in the colloid led to an improved performance of concrete, with the 50% loading ratio achieving the least penetration depth, absorption/desorption percentage, and mass loss of concrete under aggravated PSA. For the silane/nano-clay composite, the low dosage of nano-clay was adequate to mitigate the damage caused by PSA on concrete.