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This paper presents an experimental study on the rheological behaviour and mechanical strength of cement pastes and mortars prepared with high-calcium sepiolite (HCSP). HCSP was used to replace 0.0%, 2.5%, 5.0%, 7.5%, 10.0%, and 15.0% of cement. The rheological behaviour of fresh specimens was investigated along with the yield stress and plastic viscosity, which were approximated using the Bingham plastic model. Tests were also conducted to investigate the compressive strength, flexural strength, and drying shrinkage of hardened specimens. The results showed that the addition of HCSP has an adverse effect on the rheological behaviour of fresh specimens. The compressive strength and flexural strength are highest for specimens with an HCSP content of 7.5% but this is somewhat negated by the high drying shrinkage values. In contrast, the drying shrinkage values are lowest for specimens with the highest HCSP content (15.0%). It can be concluded that HCSP is a potential cement replacement material, but it is necessary to improve the workability of the fresh specimens and reduce drying shrinkage of the hardened specimens before this mineral can be used in the production of structural concrete.

The mechanical properties and setting time of magnesium oxysulfate cement (MOS) were evaluated in the context of three-dimensional printing. MOS samples with MgO-to-magnesium sulfate mole ratios ranging from 2 ~ 9 and four water-to-solid weight ratios ranging from 0.27 ~ 0.57 were developed. The initial and final setting time was ~30 and 40 min, respectively. Moreover, MOS was prepared for 3D printing. The MOS micro-structure was examined. The average pore diameter was less than 20 nm, and the total porosity ranged from 11.76 to 37.39%. The gel pore content (

Recycled aggregate (RA) differs from natural aggregate because the former possesses microstructure disadvantages, such as micro-cracks, weak interface transition zones, which hinder its application in pervious concrete. In this study, RA was firstly reinforced by paste-coating on the surface. Then, the relationship between paste-coating thickness with different size RA and paste with 5% silica fume fluidity, and that of paste fluidity, w/c ratio and superplasticizer (SP) dose were obtained. Finally, based on the two relationships and properties data of RA, the pervious concrete was formulated. The obtained pervious concrete presented excellent workability, a large sufficient permeability (more than 6.5 mm s−1) for draining rainwater and good mechanical resistance (28 d compressive strength reached 18.5 MPa). This indicates that the proposed method is a successful approach for mixture proportioning of pervious concrete.

In this paper, the results of an experimental program on studying the use of a carbonation process to enhance the properties of recycled aggregates are presented. Hardened concretes prepared by using different water-to-cement ratios in the laboratory, were crushed to produce recycled aggregates with different particle sizes. Before and after the laboratory carbonation process, the physical properties of the recycled aggregate, including water absorption and density were determined. The extent of CO 2 curing of the recycled aggregate was quantified by assessing the carbonation percentage of the aggregates. Carbonation resulted in reduction in water absorption values and increase in density and these showed that the properties of recycled aggregate were improved. The factors influencing the CO 2 curing process, including curing time, particle size and moisture contents of the recycled aggregate, were investigated.

This paper is an extension of the previous study to further explore the applicability of artificial neural networks ( ANNs ) in modeling the elastic modulus ( E c ) of recycled aggregate concrete ( RAC ). In this study, ANNs-I is firstly constructed by using 324 data sets collected from 21 international published literatures, which are randomly divided into three groups as the training, testing and validation sets, respectively. Then ANNs-II with 16 more data sets of the authors’ own experimental results added to the learning database of ANNs-I is established to examine whether the performance of ANN can be further improved. The predicted results are compared with the experimentally determined results and that modeled by conventional regression analysis. The constructed ANNs-I and ANNs-II are also applied to other experimental data sets obtained from the authors and a third party published literature to test its applicability to recycled aggregate ( RA ) taken from different sources. The results show that the constructed ANN models can well predict the elastic modulus of concrete made with RA derived from different sources.

Durability of 36nos. externally-bonded CFRP-concrete beams was studied by monitoring the intermediate cracking (IC) processes using infrared thermography (IRT) and quasi-static direct shear test. Specimens were exposed to three elevated water temperatures (25 °C, 40 °C and 60 °C) for 5, 15 and 30 weeks. In addition to the measurement of the properties at ultimate state, this work attempts to characterize the intermediate states of the intact, softened and ruptured part during the IC debonding process. The results show that the adhesive bond layers of the 40 °C and 60 °C specimens were ruptured and softened at a force level much lower than that for the 25 °C and control specimens. This is explained by the exposure condition that the water temperature exceeded the heat distortion temperature of the adhesive layer, which accelerated the bond deterioration of the composites.

Recycled aggregates are substantially different in composition and properties compared with natural aggregates, leading it hard to predict the performance of recycled aggregate concrete and design their mix proportions. This paper aims to show the possible applicability of artificial neural networks (ANNs) to predict the compressive strength of recycled aggregate concrete. ANN model is constructed, trained and tested using 146 available sets of data obtained from 16 different published literature sources. The ANN model developed used 14 input parameters that included: the mass of water, cement, sand, natural coarse aggregate, recycled coarse aggregate used in the mix designs, water to cement ratio of concrete, fineness modulus of sand, water absorption of the aggregates, saturated surface-dried (SSD) density, maximum size, and impurity content of recycled coarse aggregate, the replacement ratio of recycled coarse aggregate by volume, and the coefficient of different concrete specimen. The ANN model, run in a Matlab platform, was used to predict the compressive strength of the recycled aggregate concrete. The results show that ANN has good potential to be used as a tool for predicting the compressive strength of recycled aggregate concrete prepared with varying types and sources of recycled aggregates.

It is generally known that the use of recycled aggregates in concrete would reduce its compressive strength and render the concrete less durable. Various methods have been attempted to compensate for the lower quality of the recycled aggregates for concrete production. In this paper, the effects of incorporating Class F fly ash in the concrete mix design to mitigate the lower quality of recycled aggregates in concrete is presented. The results show that one of the practical ways to utilize a high percentage of recycled aggregate in concrete is by incorporating 25–35% of fly ash since some of the drawbacks induced by the use of recycled aggregates in concrete could be minimized.

This paper reports the results of a durability study of the effects of exposing externally-bonded CFRP-concrete beams to three elevated water temperatures (25 °C, 40 °C and 60 °C). The effects of the heated water environments on the adhesive bonding layer between the CFRP and concrete beams were evaluated by quantifying: (1) the changes of delaminations within the adhesive bonding layer, (2) the changes in resistance to direct shear force and (3) the changes of failure mode distribution. Before the exposure, the condition of the adhesive bonding layer was inspected by infrared thermography (IRT). After exposure, the deterioration of the same bonding layer and failure mode distributions were measured by analyzing the visual photos on the failed CFRP strips. The failure modes were found to be affected largely by the combined effect of elevated temperature and moisture ingress, in which three types were identified: failure at concrete beams, at adhesive bonding layer and interface between CFRP strip and concrete. With these methods, results of 54 specimens show that the adhesive bonding layers of all the specimens had gradually deteriorated in the 40 °C and 60 °C water baths. This deterioration was due to the weakening of the adhesive bonding layers when the glass transition temperature ( T g ) or the heat distortion temperature (HDT) was approached or even exceeded, and gradual development of delaminations at adhesive bonding layer.

This study is to relate the mechanical and durability properties of high performance metakaolin (MK) and silica fume concretes to their microstructure characteristics. The compressive strength and chloride penetrability of the control and the concretes incorporated with MK or silica fume (SF) at water-to-binder ( w / b ) ratios of 0.3 and 0.5 are determined. The pore size distribution and porosity of the concretes are also measured. The effect of MK and SF on the interfacial porosity is discussed based on test results. It is found that MK concrete has superior strength development and similar chloride resistance to SF concrete, and the MK concrete at a w / b of 0.3 has a lower porosity and smaller pore sizes than the control (plain) concrete. The resistance of the concretes to chloride ion penetration correlates better with the measured concrete porosity than with the paste porosity. The differences between the measured and calculated concrete porosity is smaller for MK and SF incorporated concrete than for the control concrete, indicating an improvement in the interfacial microstructure with the incorporation of the pozzolanas. This difference is found to be related to the strength and chloride penetrability of concrete to some degree.