Hong Zhu Quan

Study on Strength and Durability of Concrete Containing Recycled Coarse Aggregate Manufactured with Various Method

This paper presents the results of experimental study on the effects of adhered mortar content on strengths and durability of concrete. Compressive, tensile and shear strengths, modulus of elasticity, drying shrinkage and carbonation were tested on concrete mixtures with the water cement ratio of 0.43, 0.50 and 0.60 using 3 kinds recycled coarse aggregate and a riversand. The test results of concrete indicated higher compressive, tensile amd shear strengths and higher modulus of elasticity for concrete using recycled corase aggregate with lower adhered mortar content, lower absorption and higher specific gravity. Recycled aggregate with higher adhered mortar content also showed significunt adverse effects on drying shrinkage and carbonation. In conclusion, the upper limit of adhered mortar content of coarse recycled aggregate to keep up the quality of aggregate and concrete equal to natural coarse aggregate and those concrete is considered to be 15%.

Effects of Adhered Mortar Content on Quality of Recycled Coarse Aggregate of Concrete

Although the adhered mortar content affects the properties of recycled aggregate concrete, there are few papers describing those effects. This paper presents the results of a series of experimental study on the effects of adhered mortar content on the quality of recycled coarse aggregate of concrete. 5 kinds recycled coarse aggregates made with heating and rubbing method, mechanical crashing method and separating lightweight particle with water stream method were tested for specific gravity, absorption and adhered mortar content. Specific gravity in oven-dried condition ranged from 2.35g/cm3 to 2.59 g/cm3, absorption ranged from 1.58% to 5.83% and adhered mortar content ranged from 8.0% to 68.4%, depending on manufacturing method of recycled aggregate. Absorption decreased linearly with the increase of specific gravity. Specific gravity decreased and absorption increased with the increase of adhered mortar content. Recycled aggregate made by heating and rubbing method showed lower adhered mortar content corresponding to lower absorption and higher specific gravity, while those made by mechanical crushing method showed higher adhered mortar content corresponding to higher absorption and lower specific gravity. In conclusion, the upper limit of adhered mortar content of recycled coarse aggregate is considered to be 15%, in order to keep up the quality of coarse aggregate and properties equal to natural coarse aggregate.

Research on Durability of High Volume Fly Ash Concrete

The paper presents the results of series of experimental studies on effects of the type and replacement ratio of fly ash to portland cement on durability of concrete. Specimens made from 28 mixes of fly ash concrete with water binder ratio of 38% to 60% and with replacement ratio of fly ash of 25% to 70% and 5 mixes of portland cement concrete with water cement ratio of 38% to 75% were tested for compressive strengths, drying shrinkage, carbonation and resistance to freezing and thawing. As a results, drying shringkage decreased with fly ash addition regardless of type and replacement ratio of fly ash. Carbonation increased with fly ash replacement ratio, and type 1 fly ash showed higher carbonation. Type 1 and tpye 2 fly ashes showed practically no change in durability factor after 300 cycles of freezing and thawing up to 55% replacement, while type 4 fly ash showed rapid reduction in durability factor up to 40% replacement ratio.

Experimental Study on the Effects of Addition of Excessive Volume of Fly Ash on Concrete Properties

This paper presents the results of experimental study on the effects of addition of excessive volume of fly ash on the strength characteristics of concrete. Crushed stone aggregate concrete with the replacement ratio of fly ash to Portland cement of 0, 10%, 20%, 30%, 40%, 60% and 80% were tested for compressive strength and modulus of elasticity at the ages of 7 days, 28 days and 91 days. The test result indicated significant reduction in compressive strength with the increase of fly ash content, indication 90% reduction at 80% fly ash replacement. Reduction in modulus of elasticity was found to be less than those of compressive strength, indicating 60% reduction at 80% fly ash replacement.

Study on the Coexistence of Porous Ecological Concrete with Plants

The effects of mix proportions on the properties of porous ecological concrete, and its coexistence with plants are discussed in this paper. In conclusion, the strength of porous ecological concrete is governed simultaneously by water cement ratio and cement content. Permeability is increased with any increment in aggregate gradation and any decrease in cement paste content. The thicknesses of concrete blocks and topsoil affect the growth of plants.

Green Roofs System with Porous Ecological Concrete

Because of its durability and strength, more and more porous concrete has been used for riverbank protection or foundations of greenery. This study described a new type of green roof system without a soil layer on the porous concrete. This paper also discussed reuse of waste (fly ash generated from thermal power stations and aggregate made of ALC panel waste) to configure a newly proposed thin-type green roof system. As a result, the pilot model of lightweight thin type porous planting foundation satisfied the dynamic strength and ensured 30% void ratio needed for viability of vegetation.

Effects of Sustained Elevated Temperature on Concrete Properties in Material Engineering and its Applications

This paper presents the results of experiment conducted to evaluate the effects of sustained elevated temperature on concrete. In this experiment, concrete with 4 types of cement, low-heat portland cement, blast-furnace slag cement and fly-ash cement were tested for strength without seal after sustained temperature exposure in the range of 20 to 300°C. Compressive strengths did not decline linearly with temperature and were minimal at around 50°C, showing 20% reduction, which associated with inter-mediate weight loss of 3%. Reductions in tensile strength and modulus of elasticity were greater than compressive strength.

Performance of Concrete at Sustained High Temperature in Material Applications

The effects of sustained high temperature on concrete properties are discussed in this paper. In this experiment, concrete with 6 types of cement were tested after high temperature exposure. Although, test procedures were the same as past literature, test results showed different tendency. The temperature of 50°C at which compressive strength was minimal were found for concrete with high-early strength and medium-heat portland cement, which concrete with other cements showed no change up to 110°C. Relationship between weight loss and compressive strength differed from past literature.

Experimental Study on Air-Entraining Capability of Fly Ash Mortar

The applicability of fly ash recently used in Japan was evaluated in this paper. The characteristics of 45 batches of fly ashes obtained in Japan in 2007 are evaluated and the results show that there were large differences in physical characteristics due to the degree of grinding of the coal and the chemical composition of coal ash. The recently evaluatiion method of fly ash in Japan is not considered to be suitable by change of methylene blue color because the chemical characteristics of Ph and ORP (oxidation reduction potential) are defferent in each fly ashes. The results of the measurement of air-entraining content in mortar show that there was a tendency when the air-entraining capability reduced with the increase of the Igloss value, the brain specific surface area value, and the BET specific surface area value. The adsorption character of the air-entraining agent can be expressed approximately by the BET adsorption formula. There was a good correlation between the air-entraining content and the BET specific surface area of fly ash, cement and fine aggregate. The high purity of limestone crushed sand with a low specific surface area is suitable for accurately evaluation for higher specific surface area of fly ash.

The Glass Phase Characterization of Coal Ash Slag

In recent years, coal power generation are strongly desired lower environmental burden, emissions of SOx, NOx, and CO2 are reduced to the level. Since high efficiency of combustion or gasification systems are discharges coal ash component of complex ashes or glassy molten slag(what is CCP), and the other point of view these CCPs are expected to be effectively used for sustainable development as component for civil engineering etc. Using the CCPs for civil engineering work, Pozzolanic reactions are very important character with hydration materials, but to measure Pozzolanic reaction by mortar test is necessary to wait very long term, waiting the new method of determine the Pozzolanic reactions. So, chemical and mineralogical investigations were carried out on these inorganic materials. The glass phase which was formed by quenching is difficult to characterize by X-ray analysis by every CCP, and discussed only how percentage of glass phases, without not good explanation of CCP reactions in each steps. So in this study, we promote the new method by optical analysis and acid extraction tests etc. In this study, three phases are distinguished, such as glass I, glass II, and crystal phase. Glass I has low flux compositions, and glass II has high flux compositions which makes the basic character of Class C ash in ASTM and Chinese GB standards.