The main objective of this study is to provide more data on the effects of expanded perlite on the mechanical properties and thermal conductivity of lightweight concrete. In the experimental program, ...mixtures were prepared by partially replacing natural aggregate by expanded perlite and as a result, unit weights of lightweight concretes in fresh state varied between 700 and 2000
kg/m
3. Water to cement ratio was kept constant in all mixtures. Compressive strength, modulus of elasticity, water absorption and capillarity coefficient of the mixtures were determined. Thermal conductivity of the specimens was also obtained. Test results show that the compressive strength and modulus of elasticity decreases with increasing in perlite content. Water absorption and sorptivity coefficient, however, increase with the higher perlite contents. The test results indicate that the thermal conductivity is substantially improved with the use of perlite and a strong relationship between thermal conductivity and unit weight is obtained.
•Data-driven 11 machine learning methods are employed to predict the shear capacity of SFRC beams.•10-fold cross-validations are performed on a data of 507 experimental results.•The XGBoost ...outperformed other models in terms of high coefficient of determination and low error.•The most important feature in shear capacity prediction is the ratio of shear span to effective depth.•Volume fraction and the type of fiber are found to have a significant influence on the shear capacity of SFRC beams.
The incorporation of steel fibers in a concrete mix enhances the shear capacity of reinforced concrete beams and a comprehensive understanding of this phenomenon is imperative to have an accurate estimation in engineering designs. Although significant studies have been carried out on shear capacity estimation, mechanics-based models are not yet available due to the complex underlying phenomenon. This paper presents a data-driven approach to the shear strength of SFRC beams and incorporates the largest database compilation of 507 experimental data. Input features considered in this study are the ratio of shear span to effective depth, concrete compressive strength, longitudinal reinforcement ratio, volume fraction, aspect ratio, and type of fiber. Eleven machine learning (ML) models, namely linear regression, ridge regression, lasso regression, decision tree, random forest, support vector machine, k-nearest neighbors, artificial neural network, XGBoost, AdaBoost, and CatBoost, are evaluated to examine their shear strength estimation of SFRC beams. The XGBoost is resulting in the most accurate predictions (85%) with the lowest root mean squared error and low mean absolute error. A study on the importance of the input parameters reveals that shear span to effective depth ratio, longitudinal reinforcement ratio, concrete strength, and volume fraction of fiber are the most influential parameters of shear strength of SFRC.
High-strength and ultra-low-permeability concrete (HSULPC) is thought to be useful as a radioactive waste package. Thus, a high confining ability is desirable. For cementitious materials, sealing of ...cracks may occur in water due to the precipitation of calcium compounds. This can affect the confining ability. In this study, the sealing of a crack in HSULPC in water was investigated using micro-focus X-ray computed tomography (CT). The sealing by precipitation occurred only around the end of the specimen. Sealed regions of the crack were identified using three-dimensional image registration and CT image subtraction of images obtained for the specimen before and after it was immersed in water to evaluate temporal changes of the sealing deposits in the crack. The sealing deposits increased as the HSULPC specimen was kept in water longer. It was concluded that cracks in HSULPC in water are sealed by precipitation.
•Push-out tests were carried out on 13 steel-plate HSC shear wall specimens with group studs.•High-strength concrete/recycled aggregate concrete is used.•Replacement of some studs with tie bar ...connectors is considered.•The bond-slip constitutive relationship of specimens is given.
Steel-plate-reinforced concrete composite shear walls have been widely used in high-rise and super-high-rise buildings. To improve the bond behaviour between the steel plate and high-strength concrete (HSC) in shear walls, 13 steel-plate HSC shear wall (SPHSCSW) specimens with group studs were designed for push-out tests. Specimens were constructed using HSC or high-strength recycled aggregate concrete (HSRAC). Concrete strength, concrete type, stud length-to-diameter ratio, and replacement of studs with tie bar connectors are considered. The influence of different parameters on the interfacial bond behaviour of specimens is discussed by analysing the load-slip curves, bond strength, and interface damage energy dissipation. The equations for the shearing capacity of studs and the interfacial bond-slip constitutive relationship under different connectors were obtained. Results show that the influence of concrete strength on the bond strength of SPHSCSWs is positively correlated, and the bond behaviour with HSRAC is similar to that of normal HSC. When the stud length-to-diameter ratio exceeds four, increasing the ratio has little effect on improving the shearing capacity, and a further increase reduces the residual bond strength. Replacing some studs with tie bars can significantly improve the residual bond strength and interfacial bond energy dissipation capacity. The proposed equations for the shearing capacity of studs in SPHSCSWs and the bond-slip constitutive relationship agree well with the test results, which can be used for engineering applications and further research.
The production of concrete leads to substantial carbon emissions (~8%) and includes reinforcing steel which is prone to corrosion and durability issues. Carbon-fiber-reinforced concrete is attractive ...for structural applications due to its light weight, high modulus, high strength, low density, and resistance to environmental degradation. Recycled/repurposed carbon fiber (rCF) is a promising alternative to traditional steel-fiber reinforcement for manufacturing lightweight and high-strength concrete. Additionally, rCF offers a sustainable, economical, and less energy-intensive solution for infrastructure applications. In this paper, structure-process-property relationships between the rheology of mix design, carbon fiber reinforcement type, thermal conductivity, and microstructural properties are investigated targeting strength and lighter weight using three types of concretes, namely, high-strength concrete, structural lightweight concrete, and ultra-lightweight concrete. The concrete mix designs were evaluated non-destructively using high-resolution X-ray computed tomography to investigate the microstructure of the voids and spatially correlate the porosity with the thermal conductivity properties and mechanical performance. Reinforced concrete structures with steel often suffer from durability issues due to corrosion. This paper presents advancements towards realizing concrete structures without steel reinforcement by providing required compression, adequate tension, flexural, and shear properties from recycled/repurposed carbon fibers and substantially reducing the carbon footprint for thermal and/or structural applications.
•Shear in monolithic and composite beams with stirrups was experimentally tested.•Slab contributed to increase composite specimens’ shear strength.•The interface between concretes modified the shear ...strength mechanism.•A mechanical model of composite specimens’ shear strength is proposed.•The proposed model well fits this test programme’s experimental results.
Precast concrete beams with cast-in-place slabs on top, namely concrete composite beams are frequently used for building concrete bridge decks. In designs, the contribution of cast-in-place slabs to shear strength tends to be omitted. However, given the vast number of existent bridges with this deck typology, significant cost savings could be made when assessing these structures if the slab’s shear strength is considered. This paper analyses how cast-in-place slab influences the shear behaviour of concrete composite beams with web reinforcement. For this purpose, an experimental programme of 18 concrete specimens with web reinforcement and rectangular cross-sections was run, in which the following parameters varied: cross-sectional depth; existence of an interface between concretes; compressive strengths of the concrete of beams and slabs; differential shrinkage between concretes. It was observed that: the slab contributed to resist shear; the existence of an interface between concretes led to a crack appearing along it that caused the transmitted shear to be divided into two load paths: one through the precast beam and another one through the slab; the slab’s concrete strength was that which mainly influenced the element’s shear strength; differential shrinkage did not reduce shear strength. Based on experimental observations, a mechanical model is proposed in this paper to assess the composite elements’ shear strength, which considers the yielding of both stirrups and the slab’s longitudinal reinforcement to be a failure criterion, which well predicted the experimental results. The shear formulations of Eurocode 2, the Level III Approximation of Model Code 2010 and the (b) Formula of ACI 318-19 offered a similar result to the herein proposed method when using the entire composite element effective depth and the weighted average of the concrete strengths of both the beam and slab estimated from the area ratio. Codes significantly underestimated specimens’ interface shear.
Serious degradation mechanisms can severely reduce the service life of concrete structures: steel reinforcement can corrode, cement matrix can be attacked, and even aggregates can show detrimental ...processes. Therefore, it is important to understand how damage can occur to concrete structures and to appreciate the timing of the actions leading to damage. Damage to Concrete Structures summarizes the state-of-the-art information on the degradation of concrete structures, and gives a clear and comprehensive overview of what can go wrong. Offering a logical flow, the chapters are ordered according to the chronological timing of the actions leading to concrete damage. The author explains the different actions or mechanisms in a fundamental manner, without too many physical or chemical details, to provide greater clarity and readability. The book describes the different causes of damage to concrete, including inappropriate design, errors during execution, mechanisms occurring during hardening of concrete, and actions or degradation mechanisms during service life (hardened concrete). The degradation mechanisms are illustrated with numerous real-world examples and many drawings and photographs taken of actual structures. Written as a textbook for students as well as a reference for professionals, this easy-to-comprehend book gives readers a deeper understanding of the damage that can occur to concrete during the construction process and service.
High performance fiber reinforced concrete is developing quickly to a modern structural material with a high potential. As for instance testified by the recent symposium on HPFRC in Kassel, Germany ...(April 2008) the number of structural applications increases. At this moment studies are carried out with the aim to come to an international recommendation for the design of structures with HPFRC. Research projects are being carried out in order to supply missing information in relevant areas. Some examples of recent research at TU Delft are given. For the preparation of an internationally acceptable design recommendation for HPFRC a number of principles should be respected. The code should as much as possible be in harmony with the code for conventional fiber concrete. Moreover it should be consistent with existing design recommendations for structural concrete. Second thoughts on the introduction of such a new code are given.
•Damaged RC slabs strengthened with UHPC layer were modeled and verified by experiments.•Two different load patterns: negative bending moment and positive bending moment.•Existed cracks in RC slab ...was modeled by geometry discontinuous before strengthening.•Two different interface modeling concepts: adhesion and friction (AASHTO) and friction only (ACI).
Ultra-high performance concrete (UHPC) has been developed as an innovative cementitious based material. It can be used for repairing and strengthening existing reinforced concrete (RC) structures because of its excellent mechanical performance, such as high tensile and compressive strengths, long-term durability, and low permeability. However, when using UHPC to strengthen existing RC structures for flexure members, there is limited information on simulating existed cracks in RC structures and considering interface modeling between RC substrate and UHPC overlay. This research developed a finite element (FE) model to investigate flexural behaviors of UHPC-RC composite slab with introducing existed cracks in RC substrate by geometry discontinuous, approximately matched with experimental results previously published by the authors. Meanwhile, based on recent research on the bond strength of UHPC to concrete, a UHPC-RC interfacial model was included in the FE model. The FE model was validated with experimental laboratory results previously published by the authors, and a good agreement was obtained between numerical and experimental results. Finally, a parameter study was conducted to investigate the strengthening effects and optimizing strengthening parameters by using the developed FE model. Results showed that the effect of existing cracks on the ultimate flexure capacity of UHPC-RC cannot be neglected, and the interface model has a precise accuracy in FE modeling.
The aim of this study is to develop structural foamed concretes by using silica fume, fly ash, and polypropylene fiber. The study presents the use of fly ash for fully replacing sand to produce ...foamed concrete. Fine silica fume and polypropylene (PP) fiber were used to improve properties of foamed concrete. Lightweight foamed concretes with a wide range of concrete densities (
800–1,500 kg/m3
) were studied mainly for compressive strength, splitting tensile strength, and drying shrinkage. The results indicate that foamed concrete with a density of
800–1,500 kg/m3
and compressive strength of
10–50 MPa
can be made by using silica fume and PP fiber. Fine silica fume and PP fiber greatly improved the compressive strength of foamed concrete. In addition, adding PP fiber significantly improved the splitting tensile strength and drying shrinkage resistance.
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