Zhi Min He

Research on Influence of Chloride Ion in Sea Sand on the Performance of Concrete

Sea sand concrete is a kind of concrete in which mixed sea sand as fine aggregate, which is large-scale application in the coastal areas in recent years, especially in Ningbo area. The sea sand solves the problem of river sand shortage, coupled with cheaper price, most of the ready-mixed concrete companies are willing to use desalted sea sand instead of river sand. Many companies even are using sea sand without any treatments.In Ningbo sea sand concrete using wide range of usage is not optimistic. This survey and analysis in Ningbo area physical characteristics of concrete using sea sand and sea-sand. On this basis, chloride simulating sea sand, mixed with desalted sea sand, not desalted sea sand mortar strength measurement, the concrete strength rule were analyzed, and discovered the early strength for the sea sand concrete by the presence of chloride.

Influence of Air Entraining Agent on Performance of Inorganic Thermal Insulating Mortar

This paper presents a laboratory study on the effect of air entraining agent on the performance of thermal insulating mortar with glazed hollow bead. The test results show that with the dosage of air entraining agent increases, the consistency of thermal insulating mortar increases, apparent density, thermal conductivity and drying shrinkage decline, However, the compressive strength greater losses owing to excessive consumption of air entraining agent; air entraining agent within a certain dosage can significantly improve the operating performance of thermal insulation mortar, increase its consistency and reduce its apparent density, thermal conductivity coefficient and drying shrinkage. Due to excessive addition of air entraining agent, the apparent density, thermal conductivity and compressive strength of thermal insulation mortar all increase. For a specific insulation mortar, there will exist the best mixing amount of air entraining agent.

Mechanical Properties of Steam-Cured Concrete with Combined Mineral Admixtures

In precast concrete elements manufacturing, steam-cured concrete incorprating 30% mineral admixtures encountered the problem of too low demoulding compressive strength. To resolve it, this paper mainly studied the influence of mineral admixtures on the compressive strength, the tensile-splitting strength and the flexural strength of the steam-cured concrete. The experimental results indicated that, compared with steam-cured concrete incorprating mineral admixtures, the later strength of steam-cured concrete incorprating 0% mineral admixtures has lower increment degree and its increment of tensile-splitting strength and flexural strength inverted to some extent. The demoulding compressive strength is too low for the high volume fly ash concrete mixtures. The problem of too low demoulding compressive strength is solved by incorprating composites of ground blast furnace slag(GBFS) and fly ash. Different varieties of mineral admixture used in the concretes can produce a certain degree of potentiation.

Research on Influence of Fly Ash on the the Microstructural Characteristics of Sea Sand Concrete

By using the electron microscope scanner, we have done some research and analysis about the internal microcosmic structure of sea sand concrete. And combined with micro-XRD analysis as well integrative thermal analysis, we made observations of the internal composition of sea sand concrete., studying the effect on which sea sand makes during concrete hydration and the effect which fly ash made on the micro-structural characteristics of sea sand concrete.

Effect of Binders Combination on Porosity of Steam-Cured Concrete

Under steam curing condition, there is significant increment in the porosity of concrete. For the purpose of reducing porosity of steam-cured concrete and improving the durability of steam-cured precast elements, this paper carried out contrastive experiments including two curing condition (steam curing and standard curing), simultaneously considering the effect of different binders type, investigated the porosity change of steam curing and standard curing concretes with mineral admixtures. The corresponding mechanism was also discussed. Results indicated that, taking replace of 30% cement with double-mixing fly ash and silica fume achieves the lowest steam-cured concrete porosity. Steam curing technological measures exert a significant influence on the steam-cured concrete unclosed top suface porosity. For the characteristics of different concrete mixtures, the same steam curing technological measures exert different influence. For the same concrete, adopting appropriate technological measures can greatly decreased the porosity of concrete surface to be exposed, especially for concrete with high water-binder ratio.

Study on the Strength of Sea Sand Concrete in Ningbo

This paper mainly explain and expounded folding compressive strength of the different types of sea sand mortar , fly ash to the sea sand concretes mortar intensity influence as well as the chloride ion content to the sea sand concretes mortar intensity influence. The pulverized fly ash has the postponement function to the sea sand concretes early strength, the chloride ion has the promoter action to the sea sand concretes early strength. 20% pulverized fly ash be good to the sea sand concretes long-term strength development influence, can achieve the goal which enhances the sea sand concretes the long-term strength . The chloride ion is greater to the concretes early strength influence, especially in previous 3 days. Along with the time development, the chloride ion influence weakens, but the pulverized fly ash enlarges to the concretes intensitys influence factor. A two-phase arrived, the final concrete strength values close to each other.

Study on the Chloride Contents of Sea Sand in Ningbo

This paper is to study the sand concrete, sand is mixed with sand as fine aggregate in concrete, in recent years by large-scale applications in the coastal areas, especially in Ningbo, a coastal river sand shortage is resolved this problem, coupled with low prices, most of the commercial concrete companies are willing to play down the use of sand instead of river sand, the paper surveys and analyzes the use of sea sand in Ningbo and the physical characteristics of sea sand, on this basis, simulates sand chloride doped, dilute sea sand, not dilute sand sea sand and fly ash concrete mortar strength was measured to analyze the strength of law, by comparison analysis, the presence of chloride in the early strength concrete sand.

Effect of Gypsum on Strength Development of Steam-Cured Concrete

The use of fly ashes for cement-replacement purposes, especially in high volumes, decreases rate of early strength development of the steam curing concrete. To resolve it, this paper developed a new steam-cured concrete incorporating fly ash and a chemical activator (gypsum). Experiments were conducted to investigate the mechanical properties at early and later ages of steam and standard curing concretes. The corresponding mechanism was also discussed by testing the microstructure of concretes. Results indicate that the demoulding compressive strength of steam curing concrete with 4% gypsum dosage can meet production requirements, and compressive strength of this concrete at later ages increase well. Compared with that of ordinary pure cement steam-cured concrete, concrete with 4% gypsum has a higher compressive strength gain rate. At an early age, addition of the gypsum can distinctly accelerate the extent of hydration of the steam curing fly ash cement systems, and thus the microstructure of concrete becomes denser. However, in standard curing condtion, the effect of gypsum is not distinct.

Effect of Mineral Admixtures on Chloride Ions Content in Concrete Repair Materials

The amount of total chloride ions in concrete used as repair materials were measured under immersion conditions. The corresponding major influencing factors under natural diffusion condition were also investigated by different testing methods. The results indicated that the amount of total chloride ion significantly varies with the water to binder ratio when the water to binder ratio varies from 0.3 to 0.55. Compared with pure cement concrete, the precipitation of chloride ions in the concrete with fly ash or ground granular blast furnace slag (GGBFS) under sigle dimensions immersion was much lower. The concrete with double adding of 10% FA and 20% GGBFS acheives the lowest value of total chloride ions content.

Chloride Ions Penetration Resistance of Steam-Cured Concrete for Railway Precast Elements

By use of ASTM C1202, this paper studied the influence of mineral admixtures on the chloride ions penetration resistance of the steam-cured concrete. The experimental results indicated that mineral admixtures improved the permeability properties of high-performance concretes, but at different rates depending on the binder type. FA required a relatively longer time to get its beneficial effect. For each 10%~40% replacement of OPC by FA in a concrete mix, the values of coulomb charge of steam-cured and standard curing concrete reduces by 8%~17% at180 days. When 30% weight of the OPC were replaced by FA and ground blast furnace slag(GBFS), the inclusion of 30% mineral admixtures provided a significant improvement to the chloride ions penetration resistance properties of steam-cured and standard curing concrete at 28 days and 180 days, especially for the combination of 10% FA and 20% GBFS (double adding).