The present article discusses the impact of the different grain sizes of sand on the ultimate stress of hand-mixed cement grouted sand modified with polycarboxylate ether-based polymer using two different test standards (ASTM and BS). The fresh and hardened properties of cement grouted sands modified with polymer up to 0.16 % of the weight of cement were tested and quantified. Five types of sand with different grain sizes were used in this study. Adding polymer decreased the water/cement ratio (w/c) by 21.9–54.1%, and it kept the flow time of the cement-based grout in the range of 18–23 s. Adding polymer creates an amorphous gel that fills the porous between the cement particles, which causes a reduction in the voids, porosity and enhanced the dry density of the cement; subsequently, the compression strength of the cement-grouted sands increased significantly. Linear and nonlinear approaches were employed to estimate the compressive strength of cement grouted sand with a different grain size of sand, w/c, amount of polymer, and curing age. The compressive strength of the cement grouted sands following the BS standard was 71 % larger than the compression strength of the same mix using the ASTM standard.
Partially replacing ordinary Portland cement (OPC) with low-carbon supplementary cementitious materials (SCMs) in blended cement concrete (BCC) is perceived as the most promising route for sustainable concrete production. Despite having a lower environmental impact, BCC could exhibit performance inferior to OPC in design-governing functional properties. Hence, concrete manufacturers and scientists have been seeking methods to predict the performance of BCC mixes in order to reduce the cost and time of experimentally testing all alternatives. Machine learning algorithms have been proven in other fields for treating large amounts of data drawing meaningful relationships between data accurately. However, the existing prediction models in the literature come short in covering a wide range of SCMs and/or functional properties. Considering this, in this study, a non-linear multi-layered machine learning regression model was created to predict the performance of a BCC mix for slump, strength, and resistance to carbonation and chloride ingress based on any of five prominent SCMs: fly ash, ground granulated blast furnace slag, silica fume, lime powder and calcined clay. A database from>150 peer-reviewed sources containing>1650 data points was created to train and test the model. The statistical performance was found to be comparable to that of existing models (R = 0.94–0.97). For the first time, the model, Pre-bcc, was also made available online for users to conduct their own prediction studies.
Abstract This study answers an important question that may arise when selecting a sustainable concrete, namely “concrete mixes containing low cement and recycled aggregates are a sustainable solution?” To answer this question, this study shows how to optimize concrete mixes in terms of technical performance, and economic and environmental life cycle. Firstly, the weight to be considered for each of these dimensions of performance depends on the concrete application (e.g. residential house and high-rise building) and on the consumer’s requirements (e.g. business as usual, green, strength, service life and cost scenarios). In this study, concrete mixes containing recycled concrete aggregates (RCA) and/or fly ash (FA) are optimized to be used in sustainable residential houses. For that purpose, the CONCRE Top methodology (developed by the same authors of this study) was applied to these concrete mixes by considering a “green scenario”. The results show that, for sustainable residential houses, the concrete mixes made with high incorporation ratios of FA and RCA are considered the best option.
It is well known that, after water, concrete and mortars are the most demanded materials worldwide [...]
Geometrically nonlinear columns have been used for a variety of reasons in buildings, and their use has become even more prevalent in our time. Much research has been carried out regarding columns and arches, but geometrically nonlinear columns have not been extensively covered. Thus, this paper sheds a light on the behaviour of nonlinear columns when subjected to loading. For that purpose, two different cases of geometrical nonlinearities were considered. These columns were modelled using a validated Finite Element (FE) model. Each of the columns was loaded up to the buckling load and the displacement was recorded. Length of the column, the included angle (i.e., shallowness or span/reach ratio) and boundary conditions were taken as variables and the behaviour of columns noted each time. Additionally, a brief review of the available guidance from building codes showed a gap when it comes to nonlinear steel columns design. The results of this study showed a similarity between these columns and arches in terms of their behaviour up to the point of buckling. A parametric study was also performed to highlight the sensitivity of this hypothesis to changes in the studied parameters
For the efficient and durable design of concrete, the role of fiber-reinforcements with mineral admixtures needs to be properly investigated considering various factors such as contents of fibers and potential supplementary cementitious material. Interactive effects of fibers and mineral admixtures are also needed to be appropriately studied. In this paper, properties of concrete were investigated with individual and combined incorporation of steel fiber (SF) and micro-silica (MS). SF was used at six different levels i.e., low fiber volume (0.05% and 0.1%), medium fiber volume (0.25% and 0.5%) and high fiber volume (1% and 2%). Each volume fraction of SF was investigated with 0%, 5% and 10% MS as by volume of binder. All concrete mixtures were assessed based on the results of important mechanical and permeability tests. The results revealed that varying fiber dosage showed mixed effects on the compressive (compressive strength and elastic modulus) and permeability (water absorption and chloride ion penetration) properties of concrete. Generally, low to medium volume fractions of fibers were useful in advancing the compressive strength and elastic modulus of concrete, whereas high fiber fractions showed detrimental effects on compressive strength and permeability resistance. The addition of MS with SF is not only beneficial to boost the strength properties, but it also improves the interaction between fibers and binder matrix. MS minimizes the negative effects of high fiber doses on the properties of concrete.
This study intends to evaluate high and low-strength concrete mixes made with high volume of fly ash (FA) and recycled concrete aggregates (RCA) from both a mechanical and economic point of view. For this purpose, the mechanical characteristics of concrete, namely compressive strength (fcm), splitting tensile strength (fctm), and modulus of elasticity (Ecm) were correlated with the cost of 1 m3 of concrete mixes, taking into account the most common scenarios (e.g., cost of the raw materials, transportation between supplier and concrete plant, and mixing procedure) in the centre of Portugal. The results show that the incorporation of FA and RCA are detrimental to the mechanical properties of concrete. Ecm is predominantly influenced by RCA, and “fcm” and “fctm” are mainly controlled by FA incorporation. However, after a given age, the rate of the strength development (fcm, fctm and Ecm) of RCA concrete containing FA significantly accelerates over time relative to the reference concrete (without FA and RCA) and to the mixes made with either RCA or FA. Furthermore, the cost of concrete does not significantly change by incorporating RCA. The use of superplasticizer (SP) significantly increases the cost of concrete. However, the higher cost of concrete due to the use of SP can be offset by replacing cement with FA. Regarding the optimization process, concrete mixes with the lowest cost may not necessarily be the optimum choice regarding cost efficiency. In fact, the mechanical properties of concrete also need to be considered to aid the decision on the optimal concrete mix. Finally, the results show that the optimum mixes in terms of cost and mechanical characteristics are mostly the ones made with simultaneous incorporation of RCA, FA, and SP, rather than with their individual incorporation.
