Effect of Coarse Aggregate Size on and Crack Opening in Normal and Relationship between Stress High Strength Concretes

Fine and coarse aggregates play an important role in the fracture of concrete. However, quantitative information available on the effect of the coarse aggregate size on the fracture properties of concrete is still limited. In the present paper, the effect of coarse aggregate size （single grade of 5～10, 10～16, 16～20 and 20～25 mm） on stress-crack opening （σ-w） relation in normal and high strength concretes （compressive strength of 40 and 80 MPa, respectively） was studied. The investigation was based on three-point bending tests implemented by fictitious crack analysis. The result shows that coarse aggregate size and cement matrix strength significantly influence the shape of σ-w curve. For a given total aggregate content, in normal strength concrete, smaller size of aggregate leads to a high tensile strength and a sharp stress drop after the peak stress. The smaller the coarse aggregate, the steeper the σ-w curve. By contrast, in high strength concrete, the effect of aggregate size on σ-w relation almost vanishes. A similar σ-w relation is obtained for the concrete except for the case of 20～25 mm coarse aggregate size. The stress drop after the peak stress is more significant for high strength concrete than that for normal strength concrete. Meanwhile, the smaller the coarse aggregate size, the higher the flexural strength. Fracture energy and characteristic length increase with increasing coarse aggregate size in both normal and high strength concretes.

Evaluation the Effects of Coarse Aggregates Size on Concrete Properties

Concrete is the most generally used construction material in buildings,pavements,and infrastructures.Concrete is a construction material composed of cement as binder,fine aggregates and coarse aggregates mixed with water which hardens with time.Concrete is a versatile construction material within the housing industry of the planet.The standard of the concrete is tormented by various factors and from those various factors which may have an effect on the concrete quality are,the coarse combination size has its own nice role on the standard of concrete production.A laboratorial experiment was conducted to work out the results coarse aggregates size on recent and hardened concrete properties.For this study totally different crushed volcanic rock aggregates sizes were collected from almost Jimma city for determination of the results of coarse aggregate sizes in concrete production.Three coarse aggregate nominal sizes of 10 mm,14 mm and 20 mm were used for samples production to envision the scale effects on concrete properties.For this study the procedures that was followed,the types and quantity of materials for concrete creating were similar whereas sizes of nominal basaltic coarse aggregate were different.The fresh concrete has a slump value of 67 mm,72 mm and 83 mm for 10mm,14 mm and 20 mm aggregate sizes respectively.A total of thirty six concrete cube samples were ready and tested using compressive strength testing machine at totally different ages of the cube 7 days,14 days,and 28 days,to know their strengths.The compressive strength was 23.524 Mpa,22.643 Mpa and 22.41 MPa for aggregate sizes of 10 mm,14 mm and 20 mm respectively.The laboratory results show that 10mm coarse aggregate size gave the most effective compressive strength and comparatively lowest slump at similar water/cement ratio of 0.6.At 28th day 10mm coarse aggregate size gave 23.524 Mpa compressive strength which is the maximum compressive strength from the remainder coarse aggregates so,the optimum maximum size of coarse aggregate for this study was 10mm.

Effects of free iron oxyhydrates and soil organic matter on copper sorption-desorption behavior by size fractions of aggregates from two paddy soils

Effects of free iron oxyhydrates （Fed） and soil organic matter （SOM） on copper （Cu^2＋） sorption-desorption behavior by size fractions of aggregates from two typical paddy soils （Ferric-Accumulic Stagnic Anthrosol （Soil H） and Gleyic Stagnic Anthrosol （Soil W）） were investigated with and without treatments of dithionite-citrate-bicarbonate and of H2O2. The size fractions of aggregates were obtained from the undisturbed bulk topsoil using a low energy ultrasonic dispersion procedure. Experiments of equilibrium sorption and subsequent desorption were conducted at soil water ratio of 1：20, 25℃. For Soil H, Cu^2＋ sorption capacity of the DCB-treated size fractions was decreased by 5.9% for fine sand fraction, by 40.4% for coarse sand fraction, in comparison to 2.9% for the bnlk sample. However, Cu^2＋ sorption capacities of the H2O2-treated fractions were decreased by over 80% for the coarse sand fraction and by 15% for the clay-sized fraction in comparison to 88% for bulk soil. For Soil W, Cu^2＋ sorption capacity of the DCB-treated size fraction was decreased by 30% for the coarse sand fraction and by over 75% for silt sand fraction in comparison to 44.5% for the bulk sample. Cu^2＋ sorption capacities of the H2O2-treated fractions were decreased by only 2.0% for the coarse sand fraction and by 15% for the fine sand fraction in comparison to by 3.4% for bulk soil. However, Cu^2＋ desorption rates were increased much in H2O2-treated samples by over 80% except the clay-sized fraction （only 9.5%） for Soil H. While removal of SOM with H2O2 tendend to increase the desorption rate, DCB- and H2O2-treatments caused decrease in Cu^2＋ retention capacity of size fractions, Particularly, there hardly remained Cu^2＋ retention capacity by size fractions from Soil H after H2O2 treatment except for clay-sized fraction. These findings supported again the dominance of the coarse sand fraction in sorption of metals and the preference of absorbed metals bound to SOM in differently stabilized status among the size fractions. Thus, enrichment and turnover of SOM in paddy soils may have great effects on metal retention and chemical mobility in paddy soils.

Subsoil tillage enhances wheat productivity,soil organic carbon and available nutrient status in dryland fields

Tillage practices during the fallow period benefit water storage and yield in dryland wheat crops.However,there is currently no clarity on the responses of soil organic carbon(SOC),total nitrogen(TN),and available nutrients to tillage practices within the growing season.This study evaluated the effects of three tillage practices(NT,no tillage;SS,subsoil tillage;DT,deep tillage)over five years on soil physicochemical properties.Soil samples at harvest stage from the fifth year were analyzed to determine the soil aggregate and aggregate-associated C and N fractions.The results indicated that SS and DT improved grain yield,straw biomass and straw carbon return of wheat compared with NT.In contrast to DT and NT,SS favored SOC and TN concentrations and stocks by increasing the soil organic carbon sequestration rate(SOCSR)and soil nitrogen sequestration rate(TNSR)in the 0-40 cm layer.Higher SOC levels under SS and NT were associated with greater aggregate-associated C fractions,while TN was positively associated with soluble organic nitrogen(SON).Compared with DT,the NT and SS treatments improved soil available nutrients in the 0-20 cm layer.These findings suggest that SS is an excellent practice for increasing soil carbon,nitrogen and nutrient availability in dryland wheat fields in North China.

Investigation of the Interfacial Transition Zone between Aggregate-Cement Paste by AC Impedance Spectroscopy

Three different types and sizes of coarse aggregate were chosen,and the alternating current（AC） impedance of cement paste samples with and without aggregate was measured at different curing ages.Based on Song’s equivalent circuit model,the electrical properties from the AC impedance results were obtained,and the resistance of connected pores RCCP was used to characterize the microstructure of the interfacial transition zone（ITZ）.The results show that the RCCP of concrete sample with aggregate is lower than that of cement paste sample,which indicates that the introduction of aggregate in cement paste makes the ITZ porous.Furthermore,for the same type of aggregate,an increase in particle size leads to a more porous ITZ,which accounts for the “water effect” and a larger aggregate would accumulate a thicker water film around it.In addition,for the same size of aggregate,the physical interaction between aggregate and cement paste is dominant in early age,and the microstructure of the ITZ around limestone aggregate is denser,which mainly depends on its rough surface and high water absorption.However,the microstructures of the ITZ around granite and basalt aggregates are denser in later age,which may be due to their higher chemical activity,and the chemical interaction between them and cement paste resulting in the generation of more hydrates.AC impedance spectroscopy thus proves to be powerful for evaluation of the microstructure of the ITZ.

Calculation of Alkali Silica Reaction (ASR) Induced Expansion before Cracking of Concrete

A calculation method for predicting the formation of alkali-silica gel and analyzing the relationship of ASR induced expansion and aggregate size was proposed. The complicated chemistry of alkali silica reaction was simplified to be controlled by the diffusion process of chemical ions into reactive aggregates. The transport of chemical ions was described by the Fick＇s law. The ASR induced expansion was assumed to be directly related to the volume of produced alkali-silica gel. The finally expansion of a representative volume element （RVE） of concrete was then calculated according to the ratio of volume of alkali-silica gel and RVE. The input parameters of the model contains radius of reactive aggregate, volume fraction of reactive aggregate, initial concentration of chemical ions and porosity of cement paste. The applicability of the model was validated by an experiment of ASR-affected concrete specimens containing glass aggregate. It is shown that the amount of alkali-silica gel and ASR induced expansion can be well predicted. The expansion increasing with the decreasing aggregate size can be reproduced by the proposed model.

Soil Aggregation and Its Relationship with Organic Carbon of Purple Soils in the Sichuan Basin,China

The interaction of soil aggregate dynamics with soil organic carbon is complex with varied spatio-temporal processes in macro-and micro-aggregates. This paper is to determine the aggregation of soil aggregates in purple soils （Regosols in FAO Taxonomy or Entisols in USDA Taxonomy） for four types of land use, cropland [corn （Zea mays L.）], orchard （citrus）, forestland （bamboo or cypress）, and barren land （wild grass）, and to explore their relationship with soil organic carbon in the Sichuan basin of southwestern China. Procedures and methods, including manual dry sieving procedure, Yoder＇s wet sieving procedure, pyrophosphates solution method, and Kachisky method, are used to acquire dry, wet, and chemically stable aggregates, and microaggregates. Light and heavy fractions of soil organic carbon were separated using 2.0 g·mL^-1 HgI2-KI mixed solution. The loosely, stably, and tightly combined organic carbon in heavy fraction were separated by extraction with 0.1 M NaOH and 0.1 M NaOH-0.1M Na4P2O7 mixed solution （pH 13）. The results show that the contents of dry and wet macroaggregates 〉0.25 mm in diameter were 974.1 and 900.0 g·kg^-1 highest in red brown purple soils under forestland, while 889.6 and 350.6 g·kg^-1 lowest in dark purple soil and lowest in grey brown purple soils under cropland, respectively. The chemical stability of macroaggregates was lowest in grey brown purple soil with 8.47% under cropland, and highest in red brown purple soil with 69.34% under barren land. The content of microaggregates in dark purple soils was 587g·kg^-1 higher than brown purple soils, while 655g·kg^-1 in red brown purple soils was similar to grey brown purple soils （651g·kg^-1）. Cropland conditions, only 38.4% of organic carbon was of the combined form, and 61.6% of that existed in light fraction. Forestland conditions, 90.7% of organic carbon in red brown purple soil was complexed with minerals as a form of humic substances. The contents and stability of wet aggregates 〉 0.25 mm, contents and stability of chemically stable aggregates 〉0.25 mm, contents of microaggregates 〉 0.01 mm, contents of aggregated primary particle （d〈0.01 mm） and degree of primary particles （d 〈0.01 mm） aggregation were closely related to the concentrations of total soil organic carbon, and loosely and tightly combined organic carbon in heavy fraction. Soil microaggregation could be associated with organic carbon concentration and its combined forms in heavy fraction. There was a direct relationship between microaggregation and macroaggregation of soil primary particles, because the contents of wet aggregates 〉 0.25 mm and its water stability of aggregates were highly correlated with the contents of aggregated primary particle （d 〈 0.01 mm） and the degree of primary particles （d 〈 0.01 mm） aggregation.

An efficient approach for mesoscale fracture modeling of fully-graded hydraulic concrete

Large coarse aggregates used in fully-graded hydraulic concrete necessitate large specimens for numerical modeling.This leads to a high computational cost for mesoscale modeling and thus slows the development of multiscale modeling of hydraulic mass concrete structures.To overcome this obstacle,an efficient approach for mesoscale fracture modeling of fully-graded hydraulic concrete was developed based on the concept of the governing mesostructure.The mesostructure was characterized by a critical aggregate size.Coarse aggregates smaller than the critical size were homogenized into mortar matrices.Key issues in mesostructure generation of fully-graded hydraulic concrete are discussed,as is the development of mesoscale finite element modeling methodology.The basic concept and implementation procedures of the proposed approach are also described in detail.The numerical results indicated that the proposed approach not only significantly improves the compu-tational efficiency of mesoscale modeling but also captures the dominant fracturing mechanism at the mesoscale and reproduces reasonable fracture properties at the macroscale.Therefore,the proposed approach can serve as a basis for multiscale fracture modeling of hydraulic mass concrete structures.

Free-living nematode community structure and distribution within vineyard soil aggregates under conventional and organic management practices

Soil biota play a crucial role in soil ecosystem stability, promoting organic matter decomposition and nutrient cycling. Compared to conventional farming,organic farming is known to improve soil properties such as aggregation. Despite the importance of soil microbial communities in soil biogeochemical processes, our knowledge of their dynamics is rudimentary, especially under different agricultural management practices. Here we studied the effects of vineyard management practices(conventional and organic) and soil aggregate fractions(micro-, meso-, and macroaggregates) on free-living soil nematodes.The abundance, diversity, and ecological indices, such as the Wasilewska index and trophic diversity, of free-living soil nematodes were determined. We found that the abundance of free-living soil nematodes was increased by organic farming. In addition, plant parasites were found to increase in macroaggregates in the organic plot, which may be attributed to the weeds present due to no-tillage and no herbicides. Nematode family network connectivity increased in complexity with increasing aggregate size, highlighting the importance of the interplay between nematodes and soil inter-aggregate pore size and connectivity.

Aggregation Study of Ag-TiO_(2) Composites

Most of the toxicity data presented in the literature are obtained in relatively simple media, like distilled water. The literature reported that nanoparticles agglomerate immediately upon being added to cell culture media and if the agglomerates are used directly in antimicrobial studies, the interpretation of the toxicity results tends to be complicated. Six different molar ratios Ag-TiO2 composites were synthesized by a reduction method using two different commercial TiO2 particles as base materials and were used to find the aggregate size in distilled water and Mueller-Hinton Broth, and to obtain the minimum inhibitory concentrations (MIC) against E. coli and E. faecalis. To evaluate the evolution of the Ag-TiO2 particle size (z-average) three dilutions of each of the synthesized composites 100 μg/ml, 250 μg/mL and 500 μg/ml were realized in deionized water and Mueller Hinton broth. It was found that Ag-TiO2 composites increased in size after being diluted in Mueller-Hinton Broth, but once they grew in size, they remained constant for 24 minutes, and after this time, did not affect the MIC for the microorganisms involved.

Effects of land use patterns on soil aggregate stability in Sichuan Basin,China

Soil aggregate stability as a key indicator of soil structure, is a product of interactions between soil environment, management practices, and land use patterns. The objective of this study was to analyze the impact of various land use patterns on soil aggregate stability in Sichuan Basin of southwestern China. The dry- and water-stable aggregate size distributions were determined by manual dry sieving procedure and Yoder＇s wet sieving procedure, respectively, while microaggregates and its mechanical and chemical stabilities by Kachisky＇s method, oscillator method, and citrate-dithionate （C-D） reagent method, separately. The results indicated that fractal dimension and surface fractal dimension were useful indicators to reflect soil aggregate distribution. Land use patterns have an obvious influence on soil aggregate stability. In the study area, water stability, mechanical stability, and chemical stability followed the sequence, Barren land 〉 forestland 〉 orchard 〉 cropland, and the original stability and collapse velocity were sensitive to soil properties and soil structure. The difference of aggregate stability under different land use patterns is mainly due to the intensity of human disturbance and cultivation. Improper land use patterns will lead to breakdown of unstable aggregates, producing finer and more-easily transportable particles and microaggregates. In the future, inappropriate cultivation and land use patterns should be changed to protect soil structure, to improve soil aggregate stability and soil fertility in Sichuan Basin.

Size Effect for Normal Strength Concrete in Uniaxial Tension

This paper presents a new size effect model for normal strength concrete subjected to uniaxial tension. The model is based on two extremes, sand cement paste in uniaxial tension and a sand-cement-paste/rock interface in uniaxial tension. Uniaxial tension tests with normal strength concrete measuring the tensile strength of normal strength concrete specimens with different geometrical shapes and different ratios of the aggregate size to the characteristic dimension of the concrete specimen show a significant size effect. The theoretical size effect law prediction agrees well with the experimental data.

Characteristics of aggregate gradation, drain down and stabilizing agents in stone matrix asphalt mixtures: A state of art review

Over the years stone matrix asphalt(SMA)mixtures have evolved significantly and research works have presented some promising results.This made the paving industries to increase the usage of SMA mixtures in the pavement construction.However,SMA mixtures have certain challenges or setbacks,which require comprehensive understanding.The aim of the review paper is to present some of the challenges in SMA mixtures and their mitigations measures.It is observed that several challenges(i.e.,aggregate gradation,stone-onstone contact,drain down and stabilizing agents)related to SMA mixtures are addressed by the researchers.Many agencies have suggested their own aggregate gradation based on their experience,location,climatic conditions and available manufacturing facilities,and they are working exceptionally.Stone-on-stone contact is achieved with proper aggregate gradation and failure to meet the same will reduce the performance.Drain down is major concern in the SMA mixtures since it controls overall mixture performance.Therefore,researchers shown out the most importance to curtail the same.Several researchers followed ASTM D6390 and National Cooperative Highway Research Program(NCHRP No.424)procedure to evaluate the drain down and concluded that drain down should be less than0.3%(by weight of mixture).Apart from that,researchers are trying different stabilizing agents to reduce the drain down.Especially,stabilizing agents such as fibers and polymers have a positive impact.Recently,suitable waste and recycle products are used as stabilizing agent to reduce drain down and environmental pollution.Out of which coconut fiber has shown some promising results,however,comprehensive research is required in this regard.On the other hand,0.3%of cellulose fiber is working as a good stabilizing agent and can be used without conducting drain down test.The review paper provides a complete knowledge about different stabilizing agents used in SMA mixtures to minimize the drain down.

Destructive and non-destructive evaluation of concrete for optimum sand to aggregate volume ratio

Aggregates are the biggest contributor to concrete volume and are a crucial parameter in dictating its mechanical properties.As such,a detailed experimental investigation was carried out to evaluate the effect of sand-toaggregate volume ratio(s/a)on the mechanical properties of concrete utilizing both destructive and non-destructive testing(employing UPV(ultrasonic pulse velocity)measurements).For investigation,standard cylindrical concrete samples were made with different s/a(0.36,0.40,0.44,0.48,0.52,and 0.56),cement content(340 and 450 kg/m^(3)),water-to-cement ratio(0.45 and 0.50),and maximum aggregate size(12 and 19 mm).The effect of these design parameters on the 7,14,and 28 d compressive strength,tensile strength,elastic modulus,and UPV of concrete were assessed.The careful analysis demonstrates that aggregate proportions and size need to be optimized for formulating mix designs;optimum ratios of s/a were found to be 0.40 and 0.44 for the maximum aggregate size of 12 and 19 mm,respectively,irrespective of the W/C(water-to-cement)and cement content.

Preparation Process and Properties of Porous Ecological Concrete

By using waste bricks as aggregate,a kind of porous ecological concrete was prepared and the mixing technique and its properties were studied. Effects of the cement paste fluidity on workability of the porous ecological concrete were investigated,and influences of the water-cement ratio,the aggregate-cement ratio and the aggregate size on compressive strength and porosity of the porous ecological concrete were also discussed. Results show that for preparation of the porous ecological concrete,the aggregates should be enveloped with neat cement paste,and recommended fluidity of the cement paste is 200～235 mm. With the increasing of the aggregate-cement ratio,porosity of the porous ecological concrete increases while the 28 d compressive strength decreases. With increasing of the water-cement ratio,porosity of the porous ecological concrete decreases. And relationship between compressive strength and water-cement ratio of the porous ecological concrete does not follow Bolomey's formula. As a result of this study the porous ecological concrete is prepared,its porosity is 38.93%,the water absorption is 11.39% and the compressive strength is 1.14 MPa.

Advances in aggregatable nanoparticles for tumor-targeted drug delivery

Recent days,aggregatable nanoparticles,which can specifically respond to certain stimulus,have shown great potential in tumor-targeted drug delivery with prolonged retention and deeper penetration.In this review,we summarize recent advances in design of aggregatable nanoparticles by different stimuli.Internal(pH and enzyme)and external(light,temperature and ROS)stimuli are introduced for a comprehensive description.Moreover,the aggregated nanoparticles usually exhibit photothermal,photoacoustic,PET and enhanced MRI contrast,which is also described.In the end,we discuss about the potential applications and challenges for the future clinical translation.