Ma Baoguo

Drying Shrinkage of Cement-Based Materials Under Conditions of Constant Temperature and Varying Humidity

Abstract Currently, deformations along the central axis of specimens were usually measured under fixed environmental conditions. Seldom were the effects of environmental factors on the drying-shrinkage deformation of cement-based material considered. For this paper, the drying-shrinkage deformation at different w/b ratios and different additions to mortars was investigated under different environments at a temperature of 20 °C and humidity ranging from 100% to 50%. The specimens were cured in water for 28 days before measurement. The results illustrate that mortar shows much less shrinkage under various drying conditions when a lower w/b ratio is adopted. With a decrease in relative humidity the speed of drying-shrinkage becomes gradually lower. The addition of silica fume reduces the drying-shrinkage of mortar under higher relative humidity, because the pore structure of mortar with silica fume becomes more refined. The addition of fly ash increases the total porosity and the volume of coarse pores in the mortar. The drying-shrinkage of mortar under different conditions increases with the addition of more of fly ash.

Development of a high sound absorption material CEMCOM

Based on sound absorption mechanism of material, the special sound absorption material CEMCOM for road sound insulation is introduced. This high sound absorption material is mainly composed of expanded perlite. Using multiple sound absorption structure can improve sound absorption property of material. According to the preparation principle and durability design of material, a new kind of material with low cost and high durability is developed.

Study on mechanism of chemical activation for minerals of high belite-calcium sulfoaluminate clinker

High belite-calcium sulfoaluminate (HBCSA) cement has been developed as an eco-friendly building material, as it emits up to 35% less CO2 into the atmosphere and consume around 25% less energy in production compared with ordinary Portland cements. However, the hydraulic reactivity of C2S is low. Hence, the clinker of HBCSA activated by P2O5, B2O3, BaO, and ZnO, respectively, was studied in this paper to establish a methodology to clarify the activation mechanism. X-ray powder diffraction, scanning electron microscope, and infrared spectroscopy were used to identify the mineralogical changes in the microstructure. The results showed that the stabilizers varied a lot in the effect on microstructures of minerals. Its sequence of the effect on lattice stress of HBCSA clinker as a whole is Ba2+ > P5+ > Zn2+ > reference > B3+, the same to β-C2S mineral and cement strength at 28 days. But, there is a little difference for the sequence of their effect on , P5+ > Ba2+ > Zn2+ > Reference > B3+. The minor ionic doping activates the two minerals of β-C2S and , which are caused by disorder and defects in mineral lattice at high temperature.

Influence of Superplasticizers on Strength and Shrinkage Cracking of Cement Mortar under Drying Conditions

The effects of polynaphthalene series superplasticizers(PNS) with a low content of sodium sulfate (H-UNF),with a high content of sodium sulfate(C-UNF) and polycarboxylate type superplasticizer (PC) on strength and shrinkage cracking of cement mortar under drying conditions were investigated by means of multi-channel ellipse ring shrinkage cracking test, free shrinkage and strength test. The general effect of PNS and PC is to increase the initial cracking time of mortars, and decrease the cracking sensitivity of mortars. As for decreasing the cracking sensitivity of mortars, PC>H-UNF>C-UNF. To incorporate superplasticizers is apparently to increase the free shrinkage of mortars when keeping the constant w/b ratio and the content of cement pastes. As for the effect of controlling the volume stability of mortars, PC>C-UNF>H-UNF. Maximum crack width of mortars containing PC is lower, but the development rate of maximum crack width of mortars containing H-UNF is faster in comparison with control mortars. The flexural and compressive strengths of mortars at 28-day increase with increasing superplasticizer dosages under drying conditions. PC was superior to PNS in the aspect of increasing strength.

Influences of a New Admixture MX on Concrete Durability

The performance of concrete with a new admixture MX was studied by using the freeze-thaw cycle, permeability and chemical attack test. The experimental results show that MX improves the durability of concrete. Within the optimum proportion ranges from 0.1% to 1%, the compressive strength of concrete after freeze-thaw is increased by 20%–50%, and Young’s modulus can be increased by 3.76–5.64 times. The strength and weight loss of concrete with 0.4% MX are respectively decreased by 28% and 60% after hydrochloric acid attack. The strength and weight loss of concrete with 0.4% MX are decreased by 5%–20% after sulfuric acid and sodium sulfate attack. The permeability of concrete with 1% MX at 28 days can be decreased by more than 30%. The investigation of the negative temperature property of MX and analysis on concrete composition and microstructure by MIP reveal that the heat conduction is resisted and the freezing procedure of solution in concrete pore is retarded due to the adding of MX. Moreover, the pore structure of concrete with MX is improved, thus improving the durability. Based on this study, a resistance model of MX to block the heat and mass transference was proposed, and the mechanism of durability improvement of concrete with MX was explained.

Preparation and properties of gradient structure concrete member

Based on the dense packing powder theory, the refining and self-healing principles, and hydrophobic treatment, the special surface-layer materials and design are proposed in gradient structure concrete (GSC) member. According to service behavior, the GSC member is divided into serial structure and parallel structure. And it is fabricated corresponding to structural parameters by stacked press process, or pulled clapboard method, or suspended nets method. Use of small and full scale specimens for testing, the results are shown that: 1) the surface-layer strength of the GSC component improved by 30%, compared to that of a conventional single-layer component; 2) the width of the crack ranges from 0 to 0.1mm in the GSC component, whereas a conventional single-layer component are distributed with visible cracks(0.2–0.5mm);3) The permeating depth and chloride diffusion coefficient of the GSC component is respectively 0mm and 6.3×10–13 m2/s, whereas a conventional single-layer component is 15mm and 12.8×10–13 m2/s.

Model analysis of initial hydration and structure forming of Portland cement

The auto efficiently hydration heat arrangement and the non-contacting electrical resistivity device were used to test the thermology effect and the resistivity variation of Portland cement hydration. The structure forming model of Portland cement initial hydration was established through the systematical experiments with different cements, the amount of mixing water and the chemical admixture. The experimental results show that, the structure forming model of cement could be divided into three stages, i e, solution-solution equilibrium period, structure forming period and structure stabilizing period. Along with the increase of mixing water, the time of inflexion appeared is in advance for thermal process of cement hydration and worsened for the structure forming process. Comparison with the control specimen, adding Na2SO4 makes the minimum critical point lower, the flattening period shorter and the growing slope after stage one steeper. So the hydration and structure forming process of Portland cement could be described more exactly by applying the thermal model and the structure-forming model.

The influence of mineral functional materials on chloride ion penetration of concrete

The mechanism of chloride ion penetration in high performance concrete was analyzed. The experimental results indicate that there are two important reasons that influence the anti-chloride penetration of high performance concrete. One is the function effect of mineral functional material, so that it increases concrete’s capability to resist chloride ion penetration. The other is combined action of mineral functional material’s original capability of binding the chloride ion (physical adsorption) and physicochemical adsorption after hydration.

Effect of minor elements on silicate cement clinker

The effect of rare-earth and HX addition agent on the burn-ability of silicate cement clinker was investigated by orthogonal experiment. The result shows, compared with blank sample, f-CaO of the samples added with rare-earth and HX agent drops by 84.95%, its 3d and 28d comprssive strength enhances by 24.40% and 16.90%, respectively. It was discovered by means of X-ray diffraction and high temperature microscope analysis that sintering temperature of the sample added with rare-earth and HX addition agent is about 1320°C. At the same time, the burning temperature of tricalcium silicate desends and its crystal growth forming-rate increases. Tricalcium silicate content in burning clinker is higher and its crystal is larger.

Durability of High Performance Color Hardener

The properties of high performance color hardener (HPCH) and the mechanism were studied. HPCH is a composite system, which is composed of cementitious and auxiliary cementing materials, composite additives, abrasion resistance component (aggregate) and pigment. The porosity and pore structure of the material are obviously improved due to the activation, filling and adsorption of auxiliary cementing materials, thus resulting in a great increase of binding capacity for ions in HPCH and the obstacles of ion migrating. The density of material structure, bonding capacity of cementitious material to the abrasion-resisting component and the corrosion resistance are greatly and effectively improved by adding the auxiliary cementing materials and compound additives. According to the tests of dry shrinkage, sulphate resistance, chloride permeability and Ca(OH)2 content distribution, the property superiority of HPCH is analyzed. The mechanism of materials modification of HPCH is explained from the microscopic point of view by testing the pore structure and pore distribution via the mercury intrusion pressure method.