Concrete Substrate Research Articles

Open issues on the investigation of PBO FRCM-Concrete debonding

This paper addresses some open issues of the bond behavior of fiber-reinforced cementitious matrix (FRCM) composites applied to a concrete substrate. The study is focused on the effect of the number of fiber layers on the peak load, the effect of the loading rate on the load response, the relationship between peak load and bonded length (considering also bonded lengths substantially longer than the effective bond length), and the information that can be gained by measuring the slip at the free end of the bonded composite. The FRCM composite investigated is comprised of polyparaphenylene benzobisoxazole (PBO) fibers and a polymer-modified cementitious mortar. The experimental results are compared with results from the literature. The results indicate that the peak load must be carefully interpreted considering the effect of friction (interlocking), which is observed to occur between fibers and matrix and the fibers themselves. In addition, the effect of the loading rate requires additional investigation. Finally, the peak load of specimens with two layers of PBO fiber mesh is approximately double the peak load of tests with one layer of fiber mesh if the bonded length is longer than the effective bond length determined from tests with one layer of fiber mesh.

Cohesive Crack Models and Finite Fracture Mechanics analytical solutions for FRP-concrete single-lap shear test: An overview

In the present paper we review and compare several analytical models describing the single-lap shear test, which is the most common test to determine the bonding behaviour between a strengthening FRP plates and the concrete substrate. The models are one-dimensional and formulated under the assumption that debonding occurs as a pure mode II cracking process throughout a zero-thickness interface between the FRP strip and the brittle substrate. As such, they are all amenable to an analytical treatment. The FRP-concrete interface is described by at most three parameters among the interfacial fracture energy, the tensile strength and the elastic stiffness. Particularly, we compare the effective bond length estimates provided by different models and compare them with the ones present in Design Codes. Finally, a comparison with experimental data sets available in the Scientific Literature is also given.

Experimental Investigation on Shear Behavior of the Interface between Early-Strength Self-Compacting Shrinkage-Compensating High-Performance Concrete and Ordinary Concrete Substrate.

To improve interface bonding stress, early-strength self-compacting shrinkage-compensating high-performance concrete (ESS-HPC) was selected as an excellent strengthening material to investigate by direct shear test. Tests on seventeen Z-type specimens were carried out considering the ESS-HPC and ordinary concrete substrate (OCS) compressive strength grade, the ESS-HPC curing age, the OCS surface roughness, and the ratio of steel shear dowels as the variables. A bond stress–slip model of the interface was proposed via statistical fitting. The results show that the surface roughness and ratios of steel shear dowels had the most important influence on the shear bond stress. The shear bond stress of the specimens without steel shear dowels increased by almost 15% as the ESS-HPC strength grade changed from C60 to C75. With the increase in the curing age, the shear bond stress showed a changing trend of first increasing and then decreasing. The coarser surface with the drilling method can improve the shear bond stress by 89%. To achieve a secondary increase in the shear bond stress of specimens with steel shear dowels, the minimum ratio of steel shear dowels was 0.83%. Analytical equations are proposed in combination with the CEB-FIB Model 2010 and AASHTO Model. The calculated results show reasonable agreement with the experimental results within an acceptable range.

Microbial Networks Reveal the Structure of Water Microbial Communities in Kalamaili Mountain Ungulate Nature Reserve

Water microorganisms contribute to the key components of ecosystems in dryland waters, which are extremely important for wildlife. However, the distribution patterns of water microbes across different basal water sources are still largely unknown. This study was conducted to compare microorganisms in the water bodies of different types of water sources in the Kalamaili Mountain Ungulate Nature Reserve in China. Bioinformatic analysis revealed that the undirected microbial co-existence network consisted of 15 main modules referring to different water sources, which indicated specific molecular co-existence relationships. It was found that the most dominant phyla (namely Proteobacteria, Patescibacteria, Firmicutes, Bacteroidota, and Actinobacteriota) of the molecular ecological network shared the same structures as the microbial community, which justified the construction of the network via a random network formation. Principal coordinate analysis (PCoA) based on Bray–Curtis distances revealed that there were still considerable variations among different habitats, showing separate sample clusters. Additionally, the different topological roles of subnetworks trimmed to a uniform size indicated different co-existence patterns in the microbiome. The artificially recharged water from concrete pond substrate (ARC) subnetworks had a relatively discrete co-occurrence, while the natural water sources (NRE) and artificially recharged water from earthen pond substrate (ARE) groups were more compact with giant modules. The NRE and ARE groups were also richer in microbial composition and had a higher number of species with low abundance. Consequently, concrete substrates may contribute to dysfunction in water microbiomes. Moreover, the functional diversity of the NRE and ARE groups is due to more intra-module connections and more inter-module connections, indirectly leading to a stable function resilient to external environmental influences. In conclusion, the microecology of the NRE was more stable than that of the concrete substrate, and artificial transportation had less effect on the microbial community.

Experimental investigation of heat and moisture transfer with ventilation through porous concrete with embedded coils for air conditioning

Porous concrete permits air and water transfer, while providing the necessary structural strength required for some green building design elements. To determine the potential of porous concrete as a building material with HVAC control, the heating and cooling capacity of porous concrete with embedded heating cooling coils was investigated. In this study, a novel bio-compatible porous concrete substrate was cast into cylinders with embedded water circulation piping placed during casting to control heat and moisture content. Heating and cooling control were performed by circulating water (hot/cold) through two coils of polyethylene piping, and humidity was controlled by circulating water through perforated PVC piping. Maximum heat transfer rates of 152.3 W and −104.3 W were obtained, and maximum temperature changes of 30.0 °C, and 20.0 °C were observed for heating and cooling, respectively. During humidification, relative humidity of up to 99% was achieved with a maximum mass transfer rate of 0.0836 g s−1 and an energy transfer rate of 4.05 kJ kg−1. Dehumidification demonstrated similar mass and energy transfer rates but in a reverse transfer path. The porous concrete with embedded coil showed overall heat transfer effectiveness of 0.35, and mass transfer effectiveness of 1.002. These results highlight that this newly-designed system, combining porous concrete with heating and cooling coils, has the capacity to maintain ambient temperature (16-28 °C) when challenged with an outdoor temperature ranging from −20 °C to 50 °C, regardless of relative humidity. Its potential as an energy-efficient and dual purpose structural/HVAC component merits further study.

Flexural Strengthening of Normal Strength Plain Concrete Beams using Ultra-High Performance Fiber Reinforced Concrete Strips

In recent years, the strengthening of reinforced concrete elements in existing structures has become a very important interest topic because of the demand for development structures and extending their service life. Since the ultra-high-performance fiber-reinforced concrete properties in terms of durability and strength are fully exploited, it became early in the rehabilitation and strengthening field. This paper highlights the flexural behavior of small-scale plain normal strength concrete beam strengthened in flexure by ultra-high performance fiber reinforced concrete strips at the tensile surface by adhesive epoxy material to evaluate and quantify the effect on strength in flexure. Experimental results indicated that the ultra-high performance fiber reinforced concrete strengthening strips enhanced the flexural capacity and stiffness of the normal strength concrete substrate by 369%, 364%, and 168% at crack load and 364%, 232%, and 127% at ultimate load for concrete grades 20.8, 32.6 and 43.3 MPa respectively, delayed the crack development corresponding to apply load more than 0.37, 0.97 and 1.25 kN for strips thickness 10, 15 and 20 mm respectively in all grades of concrete beam and improved beams' ductility behavior. The main important point that affects the performance of flexural strengthening concrete beams using adhesive material is the quality of the interfacial transition bonded zone of the composite system produced between the strengthening material and the existing concrete substrate.

Explicit double-phase-field formulation and implementation for bending behavior of UHPC-NC composite beams

The Phase-field model emerges as a promising method since it can automatically capture the initiation, propagation, coalescence, and branching of cracks without any tracking algorithms. Despite its success in simulating brittle and quasi-brittle cracks, tensile (mode I) and shear (mode II) fractures cannot be distinguished effectively. Moreover, the phase-field model is rarely applied to specimens at the structural level (i.e., reinforced concrete beams), due to the demanding computational cost. To address these shortfalls, two sets of phase-field variables are formulated to describe the tensile and shear fractures of concrete, respectively, through crack-direction-based decomposition of strain energy density into tensile, shear and compressive parts. Computational burdens are greatly alleviated by implementing the model with an explicit finite element solver (Abaqus/Explicit), allowing for massive parallel computing. The sensitivity analysis is performed to investigate the effects of critical parameters with a 1D numerical tensile bar. The double-phase-field model is applied to study the bending behavior of composite beams consisting of normal-strength concrete (NC) overlayer and ultra-high performance concrete (UHPC) substrate. To this end, five UHPC-NC beams, with various thickness ratios of UHPC and NC layers, were prepared and loaded to failure. District bending strengths, cracking patterns, deformation characteristics and failure modes of the four beams were revealed and discussed. It shows that the proposed model is necessary to accurately capture the bending behavior of UHPC-NC composite beams. This model is also applied to discuss the effects of critical parameters on the bending behaviors of UHPC-NC composite beams. To benefit potential users, detailed explanations regarding the data structures of input files and user subroutines (VUEL, VUMAT, VUSDFLD in Abaqus/Explicit) are given and released on GitHub repository.

---Mechanical behavior of textile reinforced alkali-activated mortar based on fly ash, metakaolin and ladle furnace slag.

The need for repair and maintenance has become dominant in the European construction sector. This, combined with the urge to decrease CO 2 emissions, has resulted in the development of lower carbon footprint repair solutions such as textile reinforced mortars (TRM) based on alkali-activated materials (AAM). Life cycle studies indicate that AAM CO 2 savings, when compared to Portland cement, range from 80% to 30%. Furthermore, in this study, recycled aggregates were considered with the aim to promote a circular economy mindset. AAM mortars formulation based on fly ash, ladle furnace slag and metakaolin were tested for compressive and flexural strength. Three out of all formulations were chosen for an analysis on the potential of these mortars to be used for TRM applications. Tensile and shear bond tests, combined with a concrete substrate, were executed as indicators of the TRM effectiveness. Scanning electron microscopy and chemical analysis based on energy dispersive X-ray spectroscopy were used to interpret the results and reveal the reasons behind the different level of performance of these composites. Results indicated that TRM based on high calcium fly ash are unsuitable for structural strengthening applications due to low bond between matrix and/or substrate and fibers. Metakaolin-based TRM showed good performance both in terms of tensile strength and bond capacity, which suggests potential as a repair mortar.

Microbial functional diversity in rhizosphere and non-rhizosphere soil of different dominant species in a vegetation concrete slope

To investigate the effects of different dominant species on the microbial functional diversity of vegetation concrete substrates, the rhizosphere and non-rhizosphere soils of three dominant species (Pennisetum alopecuroides (PA), Arthraxon hispidus (AH) and Pueraria lobata (PL)) of vegetation concrete were studied using the Biolog-Eco method at Xiangjiaba Hydropower Station. The results showed that the microbial activity and microbial functional diversity indices in the rhizosphere soil of the three dominant plants were significantly higher than those in the non-rhizosphere soil and that the microbial activity and functional diversity indices in the rhizosphere and non-rhizosphere soil of AH, as well as in the rhizosphere soil of PL, were at a high level. The carbon sources predominantly used by rhizosphere soil microbes were carbohydrates, amino acids and polymers, while the carbon sources predominantly used by non-rhizosphere soil microbes were carboxylic acids, amino acids and polymers. The governing elements of the carbon source metabolic features of the microbial community were the soil moisture content (WC), organic matter (OM), total nitrogen (TN), potential of hydrogen (pH), microbial carbon (MBC), microbial nitrogen (MBN) and microbial phosphorus (MBP). Based on a thorough examination of these aspects, it was concluded that vegetation had altered the microbial community structure and functional diversity of the vegetation concrete substrate, perhaps improving the overall metabolic activity. A. hispidus with high adaptability should be prioritized in the regeneration of vegetation on concrete slopes.

Shear behaviour of interface between normal-strength concrete and UHPC: Experiment and predictive model

Ultra-high performance concrete (UHPC) has various excellent mechanical properties and durability which make it as a suitable repair material for bridge decks repair. However, the bond shear strength between UHPC and concrete substrate is still considered as knowledge gap in the literature. In this investigation, the bond shear properties of UHPC–NSC were systematically investigated using single side shear test, and the shear bond strength and bond failure mode were obtained. Different factors including surface roughness, steel fibre type, and substrate strength which affect the bond strength of UHPC–NSC were discussed. The results suggested that for the as cast substrate surface, bond failure occurred at the interface and the floating pulp layer adhered to UHPC. For specimens with a rough surface, the debonded interface showed that the coarse aggregate on the rough surface adhered to the UHPC. There was a linear relationship between the area of substrate adhered to the UHPC overlay and the bond shear strength. The substrate roughness has a significant influence on bond strength, while the steel fibre type has only a slight influence on bond strength. Bond strength mechanical model were built to predict the interfacial shear strength. The calculated results are in good agreement with the experimental results, indicating that the model can reliably predict the UHPC–NSC interface shear strength.

Botanical concrete. Experimentation on concrete substrates for vertical greening

Botanical concrete. Experimentation on concrete substrates for vertical greening

Retrofitting RC beams using high-early strength alkali-activated concrete

Demolition of existing deteriorated structures and construction of the new structures is a costly, time-consuming, and resource-intensive process. Repair of concrete beams and strengthening techniques for existing reinforced concrete elements is a resource-saving exercise that is time-saving also. In this work, a repair material using metakaolin-based alkali-activated concrete (AAC) is developed with high early compressive strength and split tensile strength designed with proper mix proportions. The flexural strength of reinforced concrete beams was determined without the new repair material. The specimens were loaded until failure and the deflected portion of the RC beam was then confiscated using breakers. The confiscated portion is subsequently replenished with metakaolin-based AAC and flexural strength and bond characteristics were determined. Shrinkage length changes were also measured. The metakaolin-based AAC with 15% metakaolin had a high stiffness and increased flexural strength up to 14.4% compared to the specimen before repair. It also exhibited a significant bonding with the concrete substrate with less shrinkage and improved strength.

New Chemically Resistant Coating Systems with Progressive Incorporation of Hazardous Waste in Polyurethane and Epoxy Matrices.

New types of highly chemically resistant coating systems, primarily intended for concrete and metal substrates, were designed and experimentally verified in the paper. Secondary raw materials in optimal amounts, including solidified hazardous waste (e.g., end product and cement bypass dust), were used as microfillers. The polymer coating systems, containing pre-treated hazardous waste (HW), showed high abrasion resistance and excellent adhesion to metal and concrete surfaces. Based on polyurethane and epoxy resins, the coatings can be used in environments where aggressive chemical media act, such as sewers and the chemical industry. The developed polymeric coating systems showed even better properties than the compared reference coating systems. The chemical resistance of the three-layer coating systems was evaluated both visually and based on changes in mechanical properties, such as hardness and adhesion. The microstructure of the coating systems was also monitored using a digital optical microscope and a scanning electron microscope with energy dispersive X-ray analysis (SEM-EDX) after chemical stress. It was observed that the particles of HW were fully incorporated into the polymer matrix of the coating systems.

Silica Bonding Reaction on Fly Ash Based Geopolymer Repair Material System with Incorporation of Various Concrete Substrates

Silica Bonding Reaction on Fly Ash Based Geopolymer Repair Material System with Incorporation of Various Concrete Substrates

Cement-Based Repair Materials and the Interface with Concrete Substrates: Characterization, Evaluation and Improvement.

Surface damages usually occur in concrete structures. In order to restore the functions and prolong the service life of concrete structures, their surface damages should be repaired in time. This paper reviews the main requirements for repair materials for concrete structures and the most used inorganic repair materials, such as cement-based materials, alkali-activated materials and polymer modified inorganic repair materials. Moreover, techniques to characterize and even improve the interfaces between these repair materials and concrete substrate are summarized. Cement-based material has the advantages of good mechanical properties and consistency with concrete substrate while having the problems of high shrinkage and low flexibility. Polymer modified materials were found as having lower shrinkage and higher flexural strength. Increasing the roughness or humidity of the surface, adding fibers and applying interfacial agents can improve the bond strength between cement-based repair materials and concrete substrates. All of these repair materials and techniques can help to build a good interfacial bonding, and mechanisms of how they improve the interface are discussed in this article. These are of great importance in guaranteeing the effectiveness of the repair of the concrete surface and to guide the research and development of new repair materials.

Experimental and analytical investigation on flexural behaviors of cast-in-place concrete-filled flexible composite tube beams

Fabric-reinforced cementitious matrix (FRCM) has become increasingly popular compared to other reinforcements materials of concrete; however, it is difficult but in urgent need to prepare FRCM-strengthened concrete members through a one-time cast-in-place construction procedure. Therefore, a novel system, i.e. concrete-filled flexible composite tube, is proposed, where the external tube is composed of geotextile mold and fabric mesh. While, this paper presents the results of a four-point bending test performed on five large-scale circular beams, and analyzed the influences of the number of layers of fabric meshes and the types of concrete substrate on the flexural behaviors. The test results indicate that the load–deflection responses are considerably improved by using more layers of fabric meshes, and can be further enhanced by adding the discrete fibers. Then, a comprehensive comparison with conventional FRCM-strengthened beams confirms that the full composite action of the concrete substrate and reinforcement layer was better achieved for the proposed system. Finally, a design model of concrete beams strengthened with FRCM on the entire circular cross section is proposed for the prediction on ultimate load, and shows a good agreement with the test results. The conclusions will pave the way for wider implementations of FRCM in practice.

3D printed cement-based repairs and strain sensors

This paper presents 3D printed strain sensors based on alkali activated cement repairs, demonstrating a fixed-cost method for remotely deploying a combined monitoring and maintenance technology for construction. Experimental protocols to quantitatively assess the compatibility of cements and 3D printing processes are defined and investigated in this paper. The strain sensing response of printed self-sensing cements is then investigated under compression and tension by monitoring changes in material electrical impedance. Gauge factors for self-sensing repairs printed onto concrete substrates were 8.6 ± 1.6 under compression, with an average adhesion strength of 0.6 MPa between printed repair and concrete substrate. Gauge factors for repairs printed onto glass fibre reinforced polymers were 38.4 ± 21.6 under tension: more variable than for concrete substrates due to incompatibilities between the repair and the polymer substrate. This proof-of-concept is a step towards monitoring and maintenance methods that are more compatible with the time and cost drivers of modern construction.

Software simulation of chloride ions penetration into composite of pre-fabricated geopolymer permanent formworks (PGPFs) and substrate concrete

Reinforced concrete structures are always at risk of corrosion. Use of pre-fabricated permanent formworks (PFs) is a new method of protecting concrete elements against environmental invaders. In this research, at first samples of substrate concrete (SC) and pre-fabricated geopolymer PFs were made to be exposed to chloride ions. Based on the obtained diffusion coefficients, the behavior of the composite of SC-PFs was simulated using COMSOL-multiphysics software. The seam between the formworks is itself vulnerable to the chloride penetration, so the performance of protective polyurethane mastic was evaluated. Finally, it was tried to determine the effect of loading on the chloride penetration. According to the results, the use of geopolymer-PFs can increase the service life of concrete structures up to about 114 years. On the other hand, by reducing every 0.5 cm of concrete cover, service life is reduced about 24%. The presence of a suitable sealant in the seam between the formworks is essential. Due to its low permeability, polyurethane has been able to minimize the risk of rebar corrosion adjacent to the seam. Also, applying loads of 0.6 and 0.8fc can increase the chloride diffusion coefficient in conventional concrete and geopolymer mixtures by about 20% and 14%, respectively.

The assessment of durability, coefficient of thermal expansion, and bonding strength of latex modified mixtures in repairing restrained concrete pavements

ABSTRACT In this study, two types of latex, Styrene–Butadiene Rubber (SBR) and Poly-Vinyl Acetate (PVA) were used as repair materials, and their various properties were examined. The assessments utilised Latex Modified Concrete (LMC) in ratios of 10%, 15%, and 20% to the weight of cement to investigate the properties of fresh and hardened concrete. The mechanical strength and durability of concrete were evaluated using porosity, water absorption, shrinkage, bonding behaviour, Coefficient of Thermal Expansion (CTE), and scaling resistance. The results indicated that LMC's mechanical properties improved, whereas its compressive strength decreased. The bonding strength between the LMC and the older concrete was more significant than between the Ordinary Portland Cement (OPC) and the substrate concrete. The SBR sample outperformed the PVA sample according to shrinkage and CTE results. Additionally, scaling resistance to deicing chemicals on concrete surfaces exposed to freezing-thawing cycles was satisfactory in concretes modified with both latexes.

Effect of sand content on bond performance of engineered geopolymer composites (EGC) repair material

Engineered geopolymer composites (EGC) have recently emerged as a greener and more environmentally friendly alternative to conventional engineered cementitious composites (ECC), achieving excellent mechanical and durability properties. This study investigated the effect of sand to binder (S/B) ratio on the bond performance of EGC repair material with concrete and steel reinforcement. The S/B ratio of EGC mixes was varied from 0.3 to 1.0, and its effect on the physical and mechanical properties was evaluated. It was found that increasing the S/B ratio decreased the micro-cracks at the EGC-concrete interface and, increased the bond strength. A direct correlation was observed between the elastic modulus of EGC and its bond strength with concrete substrate. The EGC-steel rebar pull-out strength initially increased and then decreased with the S/B ratio. The EGC repair material with S/B ratio more than or equal to 0.8 achieved the minimum EGC-concrete bond strength value of 1.5 MPa, as recommended by the BSI code.