Publications

Effect of napier grass ash on the autogenous shrinkage of low water binder ratio cement based materials

This work presents an experimental investigation on the effect of Napier grass ash (NGA) on the early age autogenous shrinkage of NGA blended cement paste with low water/binder ratio. Further burnt process was conducted on the as received raw NGA to decrease the carbon content, and comparison study was performed. Comprehensive tests were performed on the sealed samples to evaluate the behavior of autogenous shrinkage and self-desiccation in NGA blended cement pastes with low water/binder ratio 0.25. The autogenous shrinkage was conducted according to the standard method ASTM C1698. Setting time was determined by the Vicat needle apparatus according to the standard method ASTM C191. Internal RH measurement was performed to reveal the self-desiccation process of the sealed cement pastes at very early age. Considering the relationship between the self-desiccation and autogenous shrinkage of cementitious materials, a new ‘time zero’ was proposed. The effect of replacement of cement by NGA on the autogenous shrinkage of low water/binder ratio cement pastes was revealed by comparison study between the autogenous shrinkage measured from final setting time as defined in standard method ASTM C1698 and the new ‘time zero’.

Mitigation of Autogenous Shrinkage of Ultra-High Performance Concrete by Rice Husk Ash

Ultra-high performance concrete(UHPC) becomes one of promising concretes in the last decade due to its excellent per-formance such as ultra high strength,low permeability and very good durability.However,like high performance concrete,the UHPC is also subjected to high autogenous shrinkage due to a great amount of cement and silica fume used.The reduction of the autogenous shrinkage is an important task in the field of cement and concrete research.In this work,the rice husk ash(RHA) as an agriculture waste was used to mitigate the autogenous shrinkage of UHPC.The results show that RHA with a high content of amorphous SiO2 and the special porous structure.When 20% RHA with particle size of 5.6 μm was used,the shrinkage of UHPC was eliminated after curing for 15 d.RHA used in UHPC can reduce the cost,improve the early age properties of the UHPC and increase the environ-mental benefits because RHA has high content of atmorphous SiO2 and special structure.

Modeling of the chloride diffusivity of ultra-high performance concrete with a multi-scale scheme

Cracking Potential of Alkali-Activated Concrete Induced by Autogenous Shrinkage

Application of a pore-scale reactive transport model to study the influence of pore network characteristics on calcium leaching in cementitious systems

Multi-scale Approach from Atomistic to Macro for Simulation of the Elastic Properties of Cement Paste

A reappraisal of the ink-bottle effect and pore structure of cementitious materials using intrusion-extrusion cyclic mercury porosimetry

The changes of neurohormones after endurance exercise training in the patients with chronic heart failure

Objective To investigate the effects of endurance exercise training on plasma arginine vasopressin,atrial natriuretic peptide,angiotensinⅡ and aldosterone levels in chronic heart failure patients.Methods 12 chronic heart failure patients (coronary heart disease,New York Heart Association classⅡorⅢ) underwent supervised endurance exercise training on alternate days during a 120 days period.Before and after endurance exercise training,these neurohormones were measured by radioimmunoassay in resting condition and after peak treadmill exercise.Results After endurance exercise training for 120 days,the resting neurohormones levels were reduced significantly(P0.05),but the plasma neurohormones levels after peak treadmill exercise did not change significantly(P0.05).Conclusion The endurance exercise training could reduce the resting plasma arginine vasopressin,atrial natriuretic peptide,angiotensinⅡand aldosterone levels in chronic heart failure patients.The reduction in circulating neurohormones may delay the progress of chronic heart failure.

Characterization of cogeneration generated Napier grass ash and its potential use as SCMs

Alkali-Activated Materials as Alternative Binders for Structural Concrete: Opportunities and Challenges

Alkali-activated materials (AAMs, also called geopolymers) are considered as excellent alternative binders to replace Portland cement in concrete because AAMs have ce-ment clinker free binders made of industrial by-products or treated and cleaned wastes containing minerals via alkali-activation technology [...]

Improvement of tension control system of universal roughing mill for H-beam section

VOLUME STABILITY OF CEMENT-BASED MATERIALS: ROUNDROBIN TESTING WITHIN COST ACTION TU1404

Examining the “time-zero” of autogenous shrinkage in high/ultra-high performance cement pastes

Microstructure-based simulation of time-dependent chloride diffusivity in saturated cement paste

For accurately predicting the service life and evaluating the durability of reinforced concrete structure exposed to chloride environments, it is highly desirable to determine the chloride diffusivity in cement paste. Because of continuous cement hydration and chloride binding during the process of chloride diffusion, chloride diffusivity varies with time. In this paper, a computational approacht for predicting the time-depending chloride diffusivity in cement paste is presented. HYMOSTRUC3D, a computer-based cement hydration model, is applied to generate the 3D microstructure of cement paste. Both of the cement hydration process and chloride binding are taken into account in the simulation of microstructure. Finite element method is applied to simulate the diffusion of chloride ions through the microstructure of cement paste and estimate the chloride diffusivity based on Fick's law. A series of statistical analysis are carried out to determine the representatieve elementary volume (REV) of cement paste. The dependences of chloride diffusivity on time and w/c ratio are investigated. Finally, the simulations are validated with the experimentally measured values obtained from the literature. The comparison indicates that the simulated values and measured vlaues are of the same order of magnitude. Moreover, the trend (shape) of simulated relationship (chloride diffusivity vs time, chloride diffusivity vs w/c ratio) fits very well with the experiments.

The Discussion about the Function of Cyclodextrin Eliminate the Astringency of the Lotus Root Juice

This article talks about the best operation condition of the astringency elimination by the cyclodextrin of the lotus root juice:as a mixture make up by 3∶7 of the α,β-cyclodextrin by mass ratio.The dosage is 2.5g/L;the pH is 8.0;the temperature is 70 centigrade;the stirring speed is 1000r/min and react time:3 hours.As a result,the quality of the lotus root juice improved definitely after the process,and the stability rose efficiently.

Sustainability aspects of cement-based material blended with micronized sand

Concrete is one of the most important construction materials in the world. However, Portland cement, one of the constituents of concrete, is responsible for about 5-10% of global CO2 emission. From sustainability point of view, it is important to search for materials which can be used to reduce or to replace Portland cement in concrete. In this study, micronized sand, with high purity SiO2, has been selected as cement replacement. Environmental impact of micronized sand was evaluated and compared with Portland cement. The footprints showed that micronized sand has much less impact than cement on environment. In all categories of sustainability, the environmental impact of sand was 2 orders of magnitude lower than that of Portland cement. It was found that the use of micronized sand as cement replacement gave a big contribution in the category “global warming”, i.e. reducing CO2 emission.

THz Fingerprints of Cement-Based Materials

To find materials with an appropriate response to THz radiation is key for the incoming THz technology revolution. Unfortunately, this region of the electromagnetic spectra remains largely unexplored in most materials. The present work aims at unveiling the most significant THz fingerprints of cement-based materials. To this end transmission experiments have been carried out over Ordinary Portland Cement (OPC) and geopolymer (GEO) binder cement pastes in combination with atomistic simulations. These simulations have calculated for the first time, the dielectric response of C-S-H and N-A-S-H gels, the most important hydration products of OPC and GEO cement pastes respectively. Interestingly both the experiments and simulations reveal that both varieties of cement pastes exhibit three main characteristic peaks at frequencies around ~0.6 THz, ~1.05 THz and ~1.35 THz, whose origin is governed by the complex dynamic of their water content, and two extra signals at ~1.95 THz and ~2.75 THz which are likely related to modes involving floppy parts of the dried skeleton.

Modelling the performance of ECC repair systems under differential volume changes

Most materials used in concrete repairs have a tendency to deform due to shrinkage, heat release at early age and ambient temperature change. The restraint of these deformations by substrate concrete induces stresses in repair systems. The stresses can lead to vertical cracking through the thickness of the repair material, peeling of the repair material from the substrate concrete and/ or delamination of the interface. ECC has been proposed to be one of the most promising repair materials. Unlike common cement-based materials ECC shows tensile strain-hardening behaviour with strain capacity in the range of 3-7%, which is hundreds of times of the strain capacity of common cement-based materials. Figure 1 shows the typical tensile stress-strain curve and the average crack width of ECC. The high ductility of ECC is achieved by multiple cracking. When ECC is used as repair material, the multiple cracking can release stresses in repair systems induced by differential volume changes. The risk of repair material in tension and interface delamination is therefore reduced. It can be expect that the use of ECC can enhance the durability of concrete repairs. This phenomenon has been demonstrated both in the laboratory and in the field. An analytical model was developed to calculate stresses in repair systems subjected todifferential volume changes. In this paper, this model will be further developed to estimate the performance of ECC repair systems under differential volume changes. The modelling results, with comparisons to experimental observations, are reported here.