Constr. Mater., Volume 3, Issue 4 (December 2023) – 14 articles

The addition or substitution of various gel materials in cement-based composites has been proven to be an effective approach in enhancing the performance of concrete. Current research focuses mainly on enhancing the toughness of concrete, but lacks discussion on the performance of alternative gel materials. Therefore, this study aims to explore the effects of partially substituting cement with fly ash and slag powder as gel materials, while incorporating a high volume fraction of micro-steel fibers (6%), on the workability and mechanical properties of self-compacting concrete. By means of rigorous experimental investigation and meticulous analysis, we comprehensively assessed the workability characteristics of self-compacting concrete, encompassing critical aspects such as filling ability, cohesion, and permeability. Additionally, we conducted an extensive evaluation of the mechanical attributes of self-compacting concrete, encompassing vital parameters, such as compressive strength, axial compressive strength, splitting tensile strength, and flexural strength. Last but not least, through a holistic integration of workability and mechanical properties, we conducted a comprehensive performance evaluation of self-compacting concrete incorporating a synergistic blend of fly ash, slag powder, and micro steel fibers. The experimental results indicate that the composite addition of fly ash and slag powder in self-compacting concrete, while compatible with up to 6% micro-steel fibers, leads to a decrease in concrete workability and an increase in cohesiveness due to the addition of micro-steel fibers. Moreover, fly ash predominantly influences the tensile properties of concrete, while the addition of slag powder significantly affects the compressive and flexural properties of concrete. Additionally, the addition of micro-steel fibers significantly improves the overall mechanical properties of concrete. Full article

Recycling aged asphalt pavement has become increasingly important due to its environmental and economic advantages. Asphalt, serving as the binding agent for aggregates, plays a crucial role in pavement integrity. The deterioration of asphalt binder properties upon aging poses a significant challenge to asphalt pavement recycling. Consequently, various rejuvenators have been developed to restore aged asphalt binder properties and facilitate pavement reclamation. Waste cooking oil (WCO) is a widely used rejuvenator that mitigates the high viscosity and brittleness of aged asphalt, preventing cracking. WCO consists of triglycerides (TG) and free fatty acids (FFA), each with distinct molecular structures. In this study, molecular dynamics simulations were employed to investigate the individual effects of 10 wt.% TG and FFA on the viscosity, self-diffusion, and microstructure of aged asphalt at 1 atm and 404 K. The results demonstrate that both TG and FFA can reduce the viscosity of aged asphalt, albeit through different mechanisms. TG and FFA, characterized by high molecular mobility when dispersed in aged asphalt, enhance its mobility and reduce its viscosity. Additionally, TG effectively disrupts preferential interactions among asphaltenes, preventing their self-aggregation. In contrast, FFA has a limited impact on reducing these interactions. Furthermore, the study delves into the entanglement behaviors of FFA and TG with varying chain lengths within aged asphalt. Shorter chain lengths, as opposed to longer ones, exhibit a lower likelihood of entanglement with other asphalt molecules, resulting in increased molecular mobility and reduced asphalt viscosity. The fundamental insights gained from this research serve as a valuable reference for the application of waste cooking oil in the recycling of aged asphalt pavement. By shedding light on underlying molecular dynamics, this study contributes to the development of more effective and sustainable approaches to asphalt recycling. Full article

Delayed ettringite formation (DEF) is a recognised durability issue in concretes where the temperature during curing has been elevated. To address the potential risk of DEF, Australian specifications for heat and steam cured concretes, such as TfNSW B80, MRTS 70, and MRS 820, restrict the maximum concrete temperature during heat or steam curing to 70 or 80 °C (depending on the jurisdiction). The wide range of road authority specifications in Australia has led to uncertainty among precast concrete manufacturers, designers, and contractors, as there is a lack of clarity on how less durable the concretes become when they breach these temperature limits. Moreover, the role of supplementary cementitious materials (SCMs) in mitigating DEF in the specifications is unclear. This paper addresses these concerns by reporting some of the outcomes from research carried out over the last 8 years at the University of Technology Sydney investigating the factors that raise the risk of deleterious DEF. The work indicates that the risk of DEF is low if the cements conform to Australian specifications (AS 3972 and ATIC-SP43). The risk is further reduced if fly ash (FA) is used as part of the binder composition. As the risk of DEF is low if a limit is placed on the alkali and sulphate contents in the cement and is further mitigated if FA is used to partially replace the cement, a more practical and standardised approach to heat cured concrete specifications across the Australian jurisdictions could be adopted. Full article

Concrete and other semi-brittle materials are pressure sensitive. Their resistance to shear depends on the confining pressure acting normal to the shear plane. This behaviour is modelled using experimentally calibrated failure criteria, such as the Mohr–Coulomb failure surface. Pressure sensitivity is also strongly evident in fibre-reinforced, strain-hardening cementitious composites (SHCC), despite the internal confinement these materials possess on account of their fibre content. However, because of the great range and variety of mixes used in such materials, no general failure criteria have yet been proposed. In this paper, the pressure-sensitive shear strength of SHCC containing short discontinuous PVA fibres is modelled with a three-parameter failure criterion. The parameters of the criterion are calibrated to the experimental results obtained from several tests that combine shear and normal pressure. These include uniaxial tension and compression, split tests, triaxial compression, and a series of push-off tests with and without reinforcement crossing the shear sliding plane. The calibration of the failure criterion explicitly accounted for the magnitude of internal confinement which is generated in the cementitious matrix in response to fibre tension. The criterion is appropriate for general purpose analysis of the stress state of SHCC, but most importantly it is used to assess the SHCC contribution to the shear strength of structural elements. Full article

The energy and environmental transition in the building sector requires the development and use of low-impact materials. Despite the growing interest in bio-based and earth-based building materials, their widespread adoption is still limited due to a lack of hindsight, as their study is relatively recent. This study aims to contribute to the development of these materials by providing an extensive overview of key contributors (authors, countries, journals) in these fields. Then, the keywords of the corresponding publications were analyzed to reveal the main topics covered to date. First, a broad scale is presented, followed by a focus on sub-categories, specifically raw materials for bio-based building materials and implementation techniques for earth-based ones. Finally, a comparative analysis, with the themes covered by composite construction materials as a whole, completes the study. Using statistical analysis coupled with bibliometric network visualization software, this study provides clear, quantifiable, and objective insights into current trends. Furthermore, it facilitates the identification of new, promising research perspectives and highlights the importance of interdisciplinary collaboration. Physics, modeling, durability and microstructure studies emerge as relevant levers for advancing the future development of these eco-friendly building materials. Full article

Herein, we conducted an experimental test on basalt fiber-reinforced concrete with a high content of construction and demolition waste and then established some mathematical models based on Taylor’s formula. The concrete was prepared by using recycled clay brick powder in place of cement and recycled coarse aggregates as a substitution for natural coarse aggregates. The basalt fiber in weight dosages of 0, 0.1, 0.3, and 0.5% was used for reinforcement. The results showed that the compressive strength of concrete declined as the content of recycled aggregates increased, while the compressive strength first increased and then decreased as the basalt fiber dosage lifted. Regarding the splitting tensile strength, the reinforcement effect of basalt fiber in concrete with a high content of recycled aggregate is more significant when compared to its to its counterpart, which contains no or fewer recycled aggregates. The concrete with 0.5% basalt fiber dosage and 100% recycled aggregate content retains an equivalent compressive strength as to that of natural aggregate concrete and has about a 90% splitting tensile strength. In addition, the cubic function in comparison to the quadratic function has a higher fitting accuracy. Full article

The corrosion of steel in post-tensioned tendons has been associated with deficient grout materials containing high free sulfate ion concentrations. In a Florida bridge in 2011, tendon corrosion failures occurred for a prepackaged thixotropic grout that had developed material segregation. However, the available grout and corrosion testing prescribed in material specifications, such as grout bleed water testing, was not able to identify the propensity or modality for the grout deficiencies and the associated steel corrosion that was observed in the field. It was of interest to identify corrosion testing methods that could prescribe grout resistance to segregation-related deficiencies that can form by aberrations in construction. The objectives of the work presented here included (1) characterizing the development of physical and chemical grout deficiencies due to excess mix water and water volume displacement, (2) developing small scale test methodologies that identify deficient grout, and (3) developing test methodologies to identify steel corrosion in deficient grout. The inverted-tee test (INT) and a modified incline-tube (MIT) test were assessed and both were shown to be useful to identify the robustness of grout materials to adverse mixing conditions (such as overwatering and pre-hydration) by parameters such as sulfate content, moisture content, electrical resistance, and steel corrosion behavior. It was shown that the different grout products have widely different propensities for segregation and accumulation of sulfate ions but adverse grout mixing practices promoted the development of grout deficiencies, including the accumulation of sulfate ions. Corrosion potentials of steel < −300 mV_CSE developed in the deficient grout with higher sulfate concentrations. Likewise, the corrosion current density showed generally high values of >0.1 μA/cm² in the deficient grouts. The values produced from the test program here were consistent with historical data from earlier research that indicated corrosion conditions of steel in deficient grout with >0.7 mg/g sulfate, further verifying the adverse effects of elevated sulfate ion concentrations in the segregated grout. Full article

Using metakaolin (MK) in concrete with magnetized water (MW) has a high possibility to enhance concrete suitability. In this study, the effect of using MK and MW on concrete characteristics was studied through testing twelve concrete mixes. Seven ratios of MK were used in this study, namely 0%, 5%, 10%, and 20%, as an alternative to cement and +5%, +10%, and +20% as a cement additive. In addition, five water magnetization methods were applied on MK concrete. In the first stage of this study, the impact of different MK ratios on the workability of concrete, compressive strength, flexural strength, and tensile strength was studied using traditional tap water (TW) as the concrete mixing water. In the second stage, the best mix (best MK ratio) from the first stage was chosen to study the effect of the water magnetization method on concrete properties and to determine the best method for water magnetization. Scanning electronic microscope (SEM) analysis was also carried out on selected mixes to closely investigate the effect of MK and MW on concrete microstructure. The results showed that the best ratio of MK in concrete was +10% (MK as a 10% cement addition), and the best water magnetization method was to pass the water through 1.6 tesla then through 1.4 tesla magnetic fields. The SEM analysis confirmed the absence of pores after using MW instead of regular TW by increasing the calcium silicate hydrate (CSH) gel and reducing calcium hydroxide (CH). Using MK and MW enhanced the compressive strength by up to 33%, 32%, and 27% at 7, 28, and 365 days, respectively, and MW enhanced the workability by up to 3% compared to that of the control mix. Full article

This paper presents the authors’ research results from an analysis of intermediate foundations as well as slab and pile foundations in the context of soil consolidation. Looking at soil as a building material that changes its properties over time is very important from the point of view of the safety of construction, implementation, and operation of building structures. In addition, soil can be parameterized in such a way as to accurately describe its possible behavior under service loading. Of great interest is the phenomenon of consolidation, which is based on the reduction of soil volume over time under constant loading. This study explores existing piles and replicates soil conditions to understand individual and grouped pile behavior in combined pile–raft foundations (CPRF). To assess pile settlement from primary and secondary consolidation phases, 13 field measurements on concrete columns in gyttja clay were conducted. Analyzing data from these tests allowed engineers to accurately calibrate a numerical model. This calibrated model was instrumental in designing high-rise buildings, ensuring stability and safety. This study emphasizes the importance of understanding soil behavior, particularly consolidation phenomena, in optimizing foundation design and construction practices. Full article

Relative humidity is a key parameter for the development of delayed ettringite formation (DEF). Here, new results of very-long-term experiments (10 years) are presented. It is observed that for a relative humidity of 96%, swelling could occur after several years but with a slower kinetics. A model coupling the kinetics of swelling with the internal relative humidity is presented. It is shown that this model can reproduce the experimental behavior. Full article

This study develops alkali-activated mine tailing (MT)-based binders containing MT as the major source material and slag (S) as a minor additive, using alkaline activators containing sodium or potassium as the cationic species. The influence of the cationic species (Na or K), slag content, alkalinity (expressed using the activator silica modulus, M_s), and alkali oxide-to-powder ratio, n, on the setting behavior, paste rheology, early-age reaction kinetics, and compressive strength development are discussed. The effects of using solid activators are also considered. Changes in M_s values have a stronger impact on setting times compared to n values, underscoring the significant role of silicate species from the activator in the initial reaction mechanisms. The type of cation and physical state of the activator (in the case of K–Si-activated systems) are found to determine the dissolution rate and mobility of ionic species in the system, resulting in significant differences in the early age reaction mechanisms (e.g., K-based activators show >2× enhancement in early heat release as compared to Na-based activators) of the alkali-activated binders prepared using the same activator parameters. The difference in the viscosities of the activator solutions strongly influences the rheological characteristics of the activated systems. MT-based binders with 28-day compressive strengths ranging from 10 to 35 MPa, which are suitable for several structural/non-structural applications, are attained. The strong dependence of the compressive strength development on the alkali activation parameters and slag content in the system presents an opportunity to develop sustainable binders, with MT as their major constituent, to provide twin benefits of recycling MT wastes and mitigating the environmental impacts associated with traditional ordinary Portland cement-based binder systems. Full article

This paper investigates the viability of using a commercially available liquid polymer (LP) in lieu of ordinary cement to stabilize soil during rammed earth (RE) construction. The scope of this study includes modifying and testing the locally available natural soil with two different LPs at various percentages. Once the optimum moisture content (OMC) of the soil with LPs was determined using the Proctor test, test samples were prepared by chemical and mechanical stabilizations. Following the curing process in an unconfined open-air laboratory environment for 7 days, soil samples were tested to determine the unconfined compressive strength (UCS) and California bearing ratio (CBR) values. The results demonstrate that the lubrication effect of polymers is different than that of water. The first polymer type yields a lower OMC compared to water, while the second polymer achieves a higher OMC. The CBR and UCS values of polymer-stabilized soils are improved for both polymer types at all dosages. The CBR values of polymer-modified soils showed as high as a 10-times improvement compared to Portland cement (PC) stabilization. A similar trend is observed for the UCS results as well. The UCS value of polymer-stabilized soils reached over 1900 psi (13 MPa), which was over 3-times higher than the UCS of PC-stabilized soil. Full article

This paper presents results from numerical simulations validated by experimental results related to the effects of dynamic soil-structure interaction (DSSI) on the dynamic response of bridges. An in-service overpass was shaken using the T-Rex, a large-amplitude mobile shaker from the National Hazards Engineering Research Infrastructure (NHERI) facilities. Studies implementing Finite Element Modeling (FEM) to develop time histories, response spectra, and eigenmodes were conducted in a forward-modeling problem setup. Two models were created to assess the DSSI effects on the dynamic response of the bridge. One model included elements that incorporate DSSI effects, while the other had fixed-base boundary conditions. The response from the DSSI FEM model matched the field results better than the fixed-base model in terms of the peak response amplitudes and identified natural frequencies and modes. The influence of a series of factors, such as the soil shear wave velocity, bridge height, bridge foundation embedment depth, and the corresponding rigidity, slenderness, and embedment ratios, on the bridge response is presented. Full article

The fresh and mechanical properties of concrete made with brick aggregates of eight different maximum aggregate sizes (MAS), i.e., 10 mm, 12.5 mm, 19 mm, 25 mm, 37.5 mm, 50 mm, 63 mm, and 75 mm, were investigated. The other parameters studied were sand-to-aggregate volume ratio (s/a) (0.40 and 0.45), W/C (0.45, 0.50, and 0.55), and cement content (375 kg/m³ and 400 kg/m³). In total, 80 different concrete mixes were studied; the perimeter of the interfacial transition zone (ITZ) along the brick aggregates was quantified with an image-analysis software and the microstructure along the ITZ was investigated using a scanning-electron microscope (SEM) to corroborate the hardened properties of the concrete. Although larger MAS leads to greater slump in concrete, its effect on hardened properties is linked to other design parameters. For a cement content of 375 kg/m³ and W/C of 0.45 and 0.50, the compressive strength of concrete increases (by up to 5%–15%) with increases in MAS of up to 37.5 mm irrespective of s/a (0.40 and 0.45) and then reduces gradually. For all other cases, the compressive strength of concrete is reduced with increases in MAS. The SEM imaging confirmed the presence of weak and porous ITZ and the deposition of ettringite in the voids left by entrapped bleed water under large aggregates. The compressive strength also increased with increases in s/a from 0.40 to 0.45, predominantly for smaller MAS. Correlations between mechanical properties of concrete and stress–strain curves are proposed for different MAS. Full article