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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.

In this study, a new bio-deposition approach was used to improve the properties of recycled concrete aggregate (RCA). The new bio-deposition approach is based on bacterially induced CaCO3 precipitation through respiration, which differs from the traditional bio-deposition treatment that produces CaCO3 by urea hydrolysis. The experimental investigation was conducted in two parts. First, the physical properties including water absorption, crushing value, and density of the bio-deposition-treated RCA were determined. Then, the workability, compressive strength, and water absorption of mortars prepared with treated RCA were determined. It was found that the bio-deposition-treated RCA had a higher density and lower crushing value and water absorption compared with untreated RCA. In case of mortar, not only the workability, but also the compressive strength improved and the water absorption decreased. Moreover, the effect of bio-deposition treatment on the RCA surface and interfacial transition zone was observed by SEM.

In this study, natural sepiolite samples were treated with hydrochloric and acetic acid solutions at three different concentrations (0.1 M, 0.5 M, and 1.0 M). The effect of acid treatment on the reactivity of natural sepiolite and the change in cement hydration following the addition of natural sepiolite were studied using X-ray diffraction, particle size distribution analysis, inductively coupled spectrometry, thermogravimetric analysis, and isothermal calorimetry. Although acid treatment leads to a slight decrease in the amorphous phase content in natural sepiolite, the reactivity of sepiolite increased. The results indicate that the increase in sepiolite reactivity most likely stemmed from the activation of the Si phase. In addition, acid-treated sepiolite can modify the hydration of cement during the early curing period and hinder the hydration of cement during the later curing period. The compressive strength of specimens with strong acid-treated sepiolite was higher compared with specimens with weak acid-treated sepiolite.

In this study, the hydration behavior of circulating fluidized bed fly ash (CFBFA) as a cementitious binder was investigated in a CFBFA-lime system. Binary mixtures of CFBFA and lime were prepared with different weight ratios, and a series of experiments were performed to evaluate the hydration behavior of the mixtures. When the mixing weight ratio of CFBFA and lime was 5:1, the prepared mixtures could reach 17 MPa at 28 days. Hydration heat curves revealed that the release heat peak related to the hydration of CFBFA appeared earlier as the content of lime increased. This likely stemmed from the release of heat by the hydration of lime. Analysis of Ca(OH)2 consumption and chemically bound water revealed that the hydration reaction of mixtures can continue for a long time after Ca(OH)2 was depleted. In addition, the main hydration products of the CFBFA-lime system were C-S-H, C-A-S-H, AFm and AFt. The micro-morphology of the hydration products changed from needles to mesh-like and then to foil-like as the lime content in mixtures increased.

In this study, the pozzolanic activity of low-grade natural sepiolite was enhanced by calcination for further utilizing as a supplementary cementitious material. Sampled sepiolite was calcinated at 400, 600, 700, 800, 900, and 1000 °C, and the calcinated sepiolite were characterized and respectively blending with pastes for examining their rheological and hydration behaviors. It was found the pozzolanic activity of sepiolite was maybe mainly determined by the active Si phase content, and 800-SP showed the highest pozzolanic activity. The rheological behaviors of fresh paste blended with sepiolite calcinated at different temperatures shows obviously different. In early curing stage, the addition of sepiolite obviously accelerated the cement hydration. But in later curing stage, comparing with U-SP, the calcinated sepiolite showed hindering effect on cement hydration, and this effect was obviously regular with the increasing calcinated temperature. Additionally, by comparing with all pastes blended with sepiolite, which blended with 800-SP showed the highest compressive strength values.

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 (

This study investigated the effect of mechanical activated waste magnetite tailing (MWMT) as a pozzolanic material substitute for cement on the properties of cement-based products. The rheological behaviour (yield stress and plastic viscosity) of fresh mortar containing MWMT was investigated and approximated using the Bingham plastic model, and the mechanical properties (flexural and compressive strength) of mortar containing MWMT were studied. Results of the Frattini and strength activity index tests showed that MWMT was a low-activity pozzolanic material, consistent with the Ca(OH)2 content and mineral composition analysis. MWMT has a beneficial effect on the rheological behaviour of fresh mortar because the low specific surface area of MWMT overcomes the adverse effect of its rough and angular particles. The mechanical properties of mortar weaken as the MWMT content increases. However, the pozzolanic activity of MWMT enhances the rate at which the strength values increase as the MWMT content increases from 28 to 90 d.

This study aims to clarify the role of bio-deposition in improving the properties of recycled concrete aggregate (RCA) to enhance its reusability. Two bio-deposition treatments were investigated (immersion and spraying). The physical properties, pore structure, and micro-morphology of the RCA were investigated both before and after treatment, and the compressive and flexural strength of mortars prepared with treated and untreated RCA were also analysed. In addition, the micro-mechanical properties of the hydration products of bio-calcium carbonate were determined. The results showed that the water absorption, porosity, and crushing values of treated RCAs were lower than those of untreated RCAs. The compressive and flexural strength of mortars made with untreated RCAs were lower than those of mortars with treated RCAs. The results show that bio-calcium carbonate and its hydration products have a positive effect on the interfacial transition zone of the mortars, thereby reducing crack widths and improving the micro-mechanical properties.