Effect of Coarse Aggregate on Characteristics of Plastic Shrinkage Cracking of Lightweight Aggregate Concrete

The grading of lightweight aggregate (LA) and its water content has an effect on the plastic shrinkage cracking of lightweight aggregate concrete (LWAC). Test results show that the water absorption of LA and the water evaporation of the concrete increased with the increment of cubage of LA, but the area of plastic shrinkage cracking of LWAC decreased. Besides, LA with high water content is beneficial to restraining the plastic shrinkage cracking of LWAC.     

A Study on Lightweight Aggregate Concrete with High Fluidity

In this paper, the influence of fly ash (FA), blast furnace slag (BS) and silica fume (SF) on the properties of lightweight aggregate concrete (LAC) with high fluidity were studied. Results show that in LAC the effects of composite additives are better than that of single additive. The slump of LAC with apparent density of 1 840 kg/m 3 could reach 267 mm and the spread 650 mm. The 28d strength is 28.8 MPa for LAC with 20% ground FA and 20% BS as additives and the shale ceramsite with bulk density of 503 kg/m 3 and crushing strength 3.1 MPa was used as aggregate. Physical properties of lightweight aggregate have significant effects on durability of the flowing LAC.     

Influence of Shrinkage Cracks on Chloride Penetration and Crabonation of Concrete

The influence of shrinkage crack on chloride ion penetration and carbonation of concrete is investigated. The concrete samples with shrinkage crack of 0.07 mm,0.1 mm,0.2 mm,0.4 mm and 0.62 mm are prepared, and both an accelerated carbonation test and Qingdao sea water corrosion test are conducted on sound concrete and cracked concretes. The depths of carbonation, the content of free chloride and total chloride in crack zone and perimeter zone of concrete are analyzed. The enperimental result shows that both free chloride and total chloride content in cracked concrete increase with the rise of the shrinkage crack width, and they are related in quadratic function. The chloride penetration velocity in crack zone is higher than that in perimeter zone of concrete. However, the increased specific surface in shrinkage crack tip improves chloride binding capacity and decreases the free chloride content in this zone. When the shrinkage crack is less than 0.07mm, the carbonation depth in crack zone is same as that of sound concrete. The chloride diffusion coefficient and the carbonation depth of cracked concrete increase limited as the shrinkage crack is less than 0.1mm, and then increase significantly with the increasing of shrinkage cracked width. Moreover, the carbonation depth in crack zone is increased by 3mm in comparison with that in perimeter zone of cracked concrete.     

Recommendations on Shrinkage and Temperature Reinforcements in Concrete Slabs

The mechanism of shrinkage cracking is discussed with a simple member, which is fully restrained and subjected only to an axial restraining force caused by shrinkage, while a simple procedure is presented for the determination of the number and spacing of the cracks and the average crack width. With the simple model, some examples are shown to compare the provisions for minimum shrinkage and temperature reinforcement in GB 50010-2002 Code, ACI 318-02 Code and AS 3600-1988 Code. The results show that the provisions in GB 50010-2002 Code are too weak in comparison with the others. Finally, some recommendations are proposed.     

Study on Autogenous Relative Humidity Change and Autogenous Shrinkage of High-Performance Concrete

Autogenous relative humidity (ARH) reduction and autogenous shrinkage (AS) due to self-desiccation are common phenomena in high performance or high-strength concrete, which are the main reasons resulting in cracking of concrete at early ages. In this paper, the effects of the ratio of water to cementitious material (w/cm), paste volume content and the combined addition of silica fume (SF) and ground blast furnace slag (GBFS) on ARH change and AS of concrete due to self-desiccation were studied, and their relationship was discussed. The results indicate that the w/cm is a main factor affecting ARH change and AS of concrete. With the reduction of w/cm, ARH change and AS of concrete increases. The combined addition of SF and GBFS also augments these properties at later ages. There is significant linear correlation between ARH change and AS of concrete with different w/cm, paste volume content and the combined addition of SF and GBFS.     

Micro structure Characteristics of Recycled Fine Aggregate and Its Concrete

The characteristics of recycled fine aggregate (RFA) and its concrete (RFAC) were analyzed by SEM, EDXA, XRD, Micro harness and nitrogen absorption. The results show that RFA is an artificial aggregate with complex compositions, certain hydration activity and high permeability. The mineral compositions of RFA include SiO2, CaCO3 and a small quantity of C2S, which has a certain hydration activity and can form hydration productions. The compaction rate of cement paste in RFAC is low because of pores in it. There is obvious interfacial transition zone (ITZ) between RFAC and cement paste, and its width is bigger than that in ordinary concrete. In addition, the values of micro hardness of the interfacial transition zone on both sides of RFA and cement paste are lower. The porous structure of the recycled fine aggregates and defects of ITZ are main reasons for big pores in RFAC, which has bad effect on impermeability of RFAC.     

Determination Analysis of Content of Aggregate Micro Fines of Middle and Low Compressive Strength Manufactured Fine Aggregate Concrete

There are some controversies on influences of stone powder on performances of concrete, and its content determination is one of the hot issues of manufactured fine aggregate (MFA) concrete. Slump and compressive strength of limestone MFA concrete were analyzed on contents of stone powder for middle-low strength and different flowability concrete. The experiment results show that there are different optimums percent of stone powder of MFA, such as 5, 10, and 20 for different types of concrete, but the water-powder ratio for them is 0.4. It is concluded that optimum percent of stone powder may be predicted by water-powder 0.4 for middle and low strength MFA concrete.     

The Effect of Admixture on Drying Shrinkage of AlkaliActivated Slag Mortar

Experiment study about the effect of different admixture on drying shrinkage of alkali-activated slag mortar. The results show that shrinkage reducing agent has some inhibit effect for the drying shrinkage of alkali-activated slag mortar. However, air entraining agent, Na2SO4and Ca(OH)2 made the drying shrinkage of alkali-activated slag mortar growth.     

Structure and Performance of the Interface Zone between Mortar and Aggregate in Cement Concrete

The interface zone between mortar and aggregate influences overall performance of concrete and is an important issue for concrete research. Focusing on the structure and performance characteristics of the interface zone in cement concrete, the development of interface research in P. R. China and elsewhere were reviewed. The research aspects discussed included interface structure and performance, study techniques, interface improvement methods, and the influence of the interface on overall concrete performance. The influential factors of structural characteristics and interface zone performance, together with both microscopic and macroscopic research techniques, were summarized. The reasons for differences in interface zone structure and performance, and its degree of influence on the overall concrete performance were analyzed. Methods for improving the interface zone were generalized, including using an interface with slag powder as inorganic material and one with an organic coupling agent. Keys to research and future directions were proposed.     

Test Study on the Synthetic Control of Shrinkage Cracking on the Base of Cement Stabilized Crushed Rock

To optimize properties of the crushed rock is a simple and effective method to control the reflective cracking.There are some measures to reduce the shrinkage of the crushed rock,such as: decreasing water content and cement percentage,reducing surface tension of water.The test study shows that shrinkage resistance of the crushed rock base can be improved by mixing with fly ash,water reducing agent and shrinkage reducing agent each other,it will be better for the crushed rock to mix with fly ash,water reducing agent and shrinkage reducing agent proportionally.     

Influence of Fine Recycled Aggregate on Physical and Mechanical Properties of Concrete

Based on a series of recycle process, waste concrete can be made into fine recycled aggregate which can be used completely or partly to compound concrete as a substitute for natural sand. But the special properties of fine recycled aggregate make the performance of concrete with fine recycled aggregate different from normal concrete. Characteristics of fine recycled aggregate and its influence on physical and mechanical properties of concrete are studied. On this basis, the influence of fine recycled aggregate on gas permeation properties, chloride permeability, and carbonation resistance of concrete are also studied. It is found that fine recycled aggregate produces a lot of defects in crushing preparation. And the compressive strength, the chloride permeability and the carbonation resistance of the concrete with fine recycled aggregate as substitution show difference from that of normal concrete.     

Influence of fine aggregate on initial shrinkage of high performance concrete

The type and percentage of sand affect the gradation of coarse fine aggregate and the amount of spare mortar in concrete, which further affects the resistance of fresh concrete to initial plastic shrinkage. Taking into account the engineering characteristics of sand in the area of Chongqing, P. R. China, three fine aggregates composed of superfine, medium, mixed and manufactured sand, are used to prepare high performance concrete (HPC). The effects of these three fine aggregates on initial plastic shrinkage crack are investigated. The results show that the HPC prepared with superfine sand possesses a higher initial shrinkage value than HPC prepared with mixed or medium sand. An optimal sand percentage is necessary to reduce the initial shrinkage cracking of HPC prepared with mixed or medium sand.     

Tests on Cracking Behaviors of Reinforced Concrete Beams Underlong- Term Sulphate Attack

In this paper,six reinforced concrete beams dismounted from their worksites under long-term sulphate attack are studied.The authors analyzed the working properties and cracking moment of the reinforced concrete beams under long-term sulphate attack,suggesting that the reinforced concrete beams under long-term sulphate attack may have more favorable cracking-resistant behavior in some circumstances.     

生物质炭对土壤团聚体微域环境及重金属污染的作用研究

生物质炭作为一种优质的土壤改良剂,由于其实现了资源的可循环利用且在农业及生态领域中有着巨大的应用价值和现实意义,因而近年来受到国内外学者的普遍关注。笔者综述了生物质炭在土壤重金属污染方面的修复作用,并从生物质炭对土壤团聚体微域环境的阳离子交换量、养分及微生物等方面的改善及影响入手,探索了生物质炭对土壤重金属污染的修复机制,研究结果表明生物质炭对土壤重金属形态及生物有效性有显著的固定及改善作用。旨在为该领域未来的研究提出展望和建议,以期为生物质炭的发展动向提供参考。     

A Mesoscopic Simulation Analysis of Interface Transition Zone Characteristics Effect on Mechanical Properties of Concrete

The concrete was equivalent to a three-ingredient compound material, which was composed by aggregate, mortar and interface transition zone (ITZ). The random aggregate model was established using the Monte Carlo method. The relation between linear stress and crack was analyzed, which was used to describe the mechanics of concrete ingredients. The extended finite element method was used to simulate the failure response to various ITZ characteristics of concrete under uniaxial tension. With the tensile strength of ITZ increasing, the tensile strength, fracture energy and ductility of concrete are enhanced. The fractured modes are altered. The concrete’s elastic modulus increases with the elastic modulus of ITZ. With the thickness of ITZ decreasing, the tensile strength, elastic modulus and fracture energy of concrete increase. The interface thickness effect on concrete is reduced.     

地膜覆盖对春菠菜的影响

地膜覆盖广泛应用于多种园艺作物,但是尚未应用于菠菜春季栽培,笔者以杂交耐寒圆叶菠菜和‘美美’2个菠菜品种为试材,研究了地膜覆盖对春菠菜的影响,以探明地膜覆盖对春菠菜发芽、生长和产量、品质的影响,为该技术的推广应用提供理论依据。研究结果表明：地膜覆盖对菠菜的发芽时间和早期生长的影响非常显著,发芽时间平均缩短了7天以上,菠菜生长早期的各项外形指标都明显增加。但是到了收获期,各项指标与对照的差异并不明显。适时揭膜有可能是有效发挥覆膜效果的关键措施。覆膜后杂交耐寒圆叶菠菜叶片的蛋白质和可溶性糖含量显著提高,其他营养成分的含量在覆膜处理和对照之间差异不显著。地膜覆盖可以促进春菠菜生长发育并且提高产量和品质。     

Deformation Analysis of Thermo Elastic Plastic on ReinforcedConcrete Structure Subjected to Fire

To investigate the mechanical behavior of reinforced concrete structure subjected to fire, the incremental thermo elastic plastic creep constitutive equations of steel and concrete in consideration of temperature and creep deformation were obtained based on different yield rules and the elastic plastic theories. The nonlinear analysis for reinforced concrete simply supported slab was carried out with consideration the variation of the mechanical properties of steel and concrete with temperature. The effectiveness and applicability of the constitutive equations were verified with the test results from relevant literature. The nonlinear analysis was employed for one bay one storey reinforced concrete frame under fire and the variation of displacement at partial nodes was analysed. It was found that the reinforced concrete structure at a high temperature would have a significant deformation. And the displacement change curves of beam column joints of reinforced concrete frame were not monotonous trend and there were inflexion points. The vertical displacement values of beam column joints were less than those at midspan of cross beam.