Concrete Overstrength: Assessment of Field Strength Seeking Insights for Overdesign Optimization

This study investigates the high contents of cementitious materials in Portland cement concrete and assesses the required (f’cr) and actual (σ) compressive strength of concrete specimens. A linear optimization technique identifies the required binder content to reach f’cr. Standard specifications have required concrete overdesign (OD) for decades, but few studies have evaluated the actual magnitude of OD from field data. The compressive strength of 958 cylinders prepared in the field represented 8200 m3 of ready-mixed concrete with 300 and 450 kg/m3 of cementitious are analyzed. The actual OD appears to be 7 to 21% higher than required. The required 28-day compressive strength of concrete was achieved in less than seven days. Therefore, the content of the cementitious materials could be reduced by 6 and 17% so that concrete could reach f’cr without cementitious overconsumption. Reducing cementitious content is recommended to improve construction quality and optimize resource utilization. Among the main reasons for this recommendation are the estimated substantial long-term savings, increased concrete durability and more rational use of natural resources required to build the structures.

Durability Prediction Method of Concrete Soil Based on Deep Belief Network

To truly reflect the durability characteristics of concrete subjected to multiple factors under complex environmental conditions, it is necessary to discuss the prediction of its durability. In response to the problem of durability prediction of traditional concrete structures, there is a low prediction accuracy, and the predicted time is long, and a concrete structural durability prediction method based on the deep belief network is proposed. The influencing factors of the concrete structural durability parameters are analyzed by two major categories of concrete material and external environmental conditions, and the transmission of chloride ions in the concrete structure is described. According to the disconnection of the steel bars, the durability of the concrete structure is started, and the determination is determined. The concrete structural antiflexural strength, using a deep belief network training concrete structural antiflexural strength judgment data, constructs a concrete structural durability predictive model and completes the durability prediction of the concrete structure based on the deep belief network. The proposed prediction method based on the deep belief network has a high prediction accuracy of 98% for the durability of concrete column structures. The simulation results show that the concrete structural durability’s prediction accuracy is high and the prediction time is short. The prediction of concrete durability discussed here has important guiding significance for the improvement of concrete durability test methods and the improvement of concrete durability evaluation standards in China.

Evaluation of Concrete Durability Based on Cloud Model and D-S Evidence Theory

The environment in alpine region is complex and harsh, and the durability of concrete is seriously affected by freeze-thaw and salt invasion. In this paper, the relative dynamic modulus of elasticity, chloride permeability coefficient, mass loss rate and carbonation depth are selected as the evaluation indexes of concrete durability in Northeast China. Based on prior knowledge and expert group decision-making, the durability grade is divided and the evaluation standard is established; The evaluation model of concrete durability based on cloud model and D-S evidence theory is established. According to the engineering experimental data, the membership degree of concrete durability evaluation index in different grades is obtained through the correlation measurement of cloud model. The normalized evidence is formed and fused by D-S evidence theory. The results show that the durability grade of concrete is grade I, which is consistent with the actual project. It shows that using cloud model and evidence theory evaluation model to evaluate the durability of concrete is a new and effective method.

Recent developments in reactivity testing of supplementary cementitious materials

Identification and rapid characterization of novel supplementary cementitious materials (SCMs) is a critical need, driven by shortfalls in conventional SCMs. In this study, we present a discussion of recently developed reactivity tests – the R3 test, the modified R3 test, the lime strength test, and the bulk resistivity index test. These tests measure reactivity parameters such as heat release, bound water, calcium hydroxide consumption, strength, and bulk resistivity. All tests can screen inert from reactive materials. To additionally differentiate pozzolanic and latent hydraulic materials, two parameters, for example, calcium hydroxide consumption and heat release, are needed. The influences of SCM bulk chemistry, amorphous content, and fineness on measured reactivity are outlined. Reactivity test outputs can predict strength and durability of cement paste/mortar/concrete; however, caution must be exercised as these properties are influenced by a variety of other factors independent of reactivity. Thoughts are provided on using reactivity tests to screen materials for concrete durability.

Deformations in Cement Pastes during Capillary Imbibition and Their Relation to Water and Isopropanol as Imbibing Liquids

The traditional approach for evaluating capillary imbibition, which describes the phenomena as a linear relationship between mass gain and the square root of time, considers a rigid pore structure. The common deviation from the linearity when using the square-root law (manifested in a downward curvature, i.e., slower water ingress) can be explained by considering a changing pore structure during the process caused by the swelling of calcium silicate hydrate (C-S-H) during water ingress. Analysing how the combination of deforming phase (C-S-H), non-deforming phase, and porosity affects the capillary water ingress rate is relevant for a deeper understanding of concrete durability. In this research, the C-S-H content was quantified by means of XRD diffraction coupled with Rietveld + PONKCS, dynamic water sorption (DVS), and SEM/BSE images coupled with phase mapping using PhAse Recognition and Characterization (PARC) software. The porosity was assessed by mercury intrusion porosimetry, water absorption under vacuum, and DVS. Furthermore, to assess deformations occurring with water and a non-aqueous imbibant, capillary imbibition tests with water and isopropanol as invading liquids were performed along with simultaneous deformation measurements. The relation between the relative C-S-H content and porosity has a great impact on the transport process. Samples exposed to isopropanol presented a much larger liquid uptake but significantly fewer deformations in comparison to imbibition with water. The effects of the changing pore structure were also evaluated with the Thomas and Jennings model, from which calculations indicated that pore shrink during imbibition. A comprehensive description of the relation between deformations and capillary imbibition in cement pastes reveals that liquid ingress is highly influenced by deformations.

Preparation and performance of graphene oxide/self-healing microcapsule composite mortar

To meet the unique requirements for concrete durability and resistance in power transmission projects in Northwest China. Microcapsules were created physically using sodium silicate and bentonite as the capsule core and ethyl cellulose as the capsule wall. By using graphene oxide as a conductive medium, standard specimens of cement-based materials were created. Indoor experiments and micro technology were used to determine the optimal ratio of graphene-microcapsules, study the effects of graphene content, microcapsule content, and curing age on compressive strength, resistance, and self-repairing effect of the composite material. The average microcapsule size was 1.25 mm, according to the findings. The microcapsule was a relatively regular sphere with a rough surface and dense structure. The recommended content was 2% microcapsules and 0.1% graphene oxide. The compressive strength first increased and then decreased as the number of microcapsules and graphene oxide increased, and the resistance gradually increased. The repairing rate of compressive strength was 57% after the cracks were repaired, and the recovery rate was 81%.

Evaluation of synergic methods for corrosion protection of reinforced steel

Purpose This study aims to evaluate the effect of pH on the reinforced concrete steel protection for rebars coated with paint formulations containing talc and free from it. As the presence of talc in paints can offer high pH which cordially affects the protection behavior of the coated rebars. Additionally, this study includes evaluating the durability of concrete mixes in presence of some replacements of ordinary cement such as meta-kaolin (MK) and ground granulated blast furnace slag (GGBFS). Design/methodology/approach Two paint formulations were prepared containing the same ingredients except that (P1) is free from talc and (P2) contains talc. The anticorrosive behavior of painted steel in the blended concrete mixes containing MK and GGBFS was studied by using different electrochemical techniques in chloride solution. The concrete durability was evaluated by the means of compressive and bond strength beside chloride permeability. Different concrete mixes containing mineral groups or pozzolanic materials were prepared by replacing (10, and 30%) GGBFS and (5, 10 and 15%) MK as binary from cement CEM I with (w/b) 0.45 with superplasticizer ratio (SP) 2% of the binder Findings It was found that the presence of talc, in spite of its ability to offer high pH, has affected positively the corrosion behavior of reinforced concrete steel by forming a complex with concrete even if it is present in paint formulation and not free in the medium. Originality/value The results revealed that concrete blended with (30% GGBFS and 10% MK) with coated rebars with P2 containing talc showed the highest corrosion protection performance in addition to modified permeability and compression resistance.

Study on Metakaolin Impact on Concrete Performance of Resisting Complex Ions Corrosion

The main purpose of this study is to determine the metakaolin (MK) impacts on the concrete durability when the concrete is subjected to joint corrosion of SO42−,Mg2+ and, Cl−. Four groups of concrete test samples, which contained different MK contents, were designed and tested in order to see their physical property changes and macro-morphology differences during the cyclic corrosion process. And a series of approaches, including XRD, FTIR, SEM, and EDS, were applied to study the concrete phase composition changes and the micro-morphology features of all groups. According to the test results, when reaching 20 cycles, the concrete sample with 10% MK showed the best concrete physical properties; when reaching 120 cycles, the concrete with 5% MK content showed the best durability, produced similar amount of corrosion products to ordinary concrete, and presented relatively compacted micro-structure and small internal porosity. Mg2+ actually has a great impact on metakaolin. The corrosion product quantity increased significantly when MK admixture reached 15%. Due to the great number of produced M-S-H, the corrosive ions damaged the concrete for a second time, leading to serious aggregate peeling-off, powder surface of test samples, and porous micro-structure.

Effects of GO/Al2O3 and Al2O3 Nanoparticles on Concrete Durability against High Temperature, Freeze-Thaw Cycles, and Acidic Environments

In this paper, the effect of GO/Al2O3 and Al2O3 synthesized nanoparticles on the durability of concrete is studied. To this end, after the synthesis of nanoparticles and confirmation of nanoparticles fabrication by SEM and FT-IR spectra, three concrete samples for each experiment related to each mix design were prepared and subjected to freeze-thaw cycles, high temperature, and acidic environment. The results show that the samples containing GO/Al2O3 nanoparticles had the least weight loss in freeze-thaw cycles as well as better resistance against acidic environment and the lowest apparent changes at high temperature compared to the samples containing nano-Al2O3 and the samples without nanoparticles. The replacement of 2 wt.% of cement with GO/Al2O3 nanoparticles results in the highest increase in concrete durability. The presence of nanoparticles in the concrete microstructure and the validation of the results are investigated by FT-IR, SEM, and EDX spectra.

Water Absorption of Incorporating Sustainable Quarry Dust in Self-Compacting Concrete

In construction industry nowadays, self-compacting concrete (SCC) is a concrete technology innovation which gives more benefits over conventional concrete. SCC was invented to improve concrete durability without using any vibrator while placing it into formwork. In order to conserve natural sand, quarry dust (QD) as a waste and sustainable material has been incorporated to replace fine aggregate in SCC. In this study, conventional concrete and quarry dust in self-compacting concrete (QDSCC) mixes consist of 0%, 10%, 20%, 30%, 40% and 50% QD were prepared. The workability test was conducted to determine the performance of fresh concrete and ensuring all the QDSCC properties follow the acceptance criteria for SCC. Meanwhile, the hardened concrete specimens were water cured for 7, 28 and 60 days to conduct water absorption test. This research aim is to determine water absorption of incorporating sustainable QDSCC. Thus, it resulted that 50% of QDSCC has achieved the lowest water absorption of QDSCC as compared to other dosages. Finally, sustainability in concrete technology can be promoted by incorporating QDSCC.