Pumpability of Manufactured Sand Self-compacting Concrete

By the addition of superplasticizer and air entraining agent,manufactured sand selfcompacting concrete(MS SCC)with slump flow varying from 500 to 700 mm and air content varying from 2.0%to 9.0%were prepared and the pumpability of MS SCC was studied by a sliding pipe rheometer(Sliper).According to the Kaplan’s model,the initial pump pressure and the pump resistance of MS SCC were obtained.Meanwhile,rheological properties including the yield stress and the plastic viscosity of MS SCC were measured by a rheometer.The experimental results show that the increase of slump flow contributes to a higher pumpability and a proper air content,i e,6%is beneficial for the pumpability of MS SCC.Due to the existence of stone powder and stronger angularity of MS,the initial pump pressure of MS SCC is only about 60%-88%that of river sand(RS)SCC with the same slump flow and air content,indicating that MS SCC possesses a higher pumpability than RS SCC.

An Investigation into the Compressive Strength,Permeability and Microstructure of Quartzite-Rock-Sand Mortar

River sand is an essential component used as a fine aggregate in mortar and concrete.Due to unrestrained exploitation,river sand resources are gradually being exhausted.This requires alternative solutions.This study deals with the properties of cement mortar containing different levels of manufactured sand(MS)based on quartzite,used to replace river sand.The river sand was replaced at 20%,40%,60%and 80%with MS(by weight or volume).The mechanical properties,transfer properties,and microstructure were examined and compared to a control group to study the impact of the replacement level.The results indicate that the compressive strength can be improved by increasing such a level.The strength was improved by 35.1%and 45.5%over that of the control mortar at replacement levels of 60%and 80%,respectively.Although there was a weak link between porosity and gas permeability in the mortars with manufactured sand,the gas permeability decreased with growing the replacement level.The microstructure of the MS mortar was denser,and the cement paste had fewer microcracks with increasing the replacement level.

Effect of Methylene Blue (MB)-value of Manufactured Sand on the Durability of Concretes

The relation between the methylene blue （MB） value of MS and its limestone powder content and clay content was investigated. The effects of MB values ranging from 0.35 to 2.5 on the workability of fresh concrete, the mechanical properties, the resistance to freezing as well as the resistance to chlorine ion permeation of the hardened concrete were all investigated. The experimental results showed that the MB value had no correlation with the limestone powder content of MS, while it was directly related to the clay content. With an increase of MB value, concrete workability decreased, as did the flexural and 7-day compressive strengths, however, the 28-day compressive strength was not affected. Furthermore, influence of MB value on concretes of different strength levels was different. For low-strength concretes, an increase of MB value could improve its impermeability, but this was not the case for high-strength concretes. Instead, their resistance to chloride ion permeability decreased slightly. However, even a slight increase in MB value remarkably accelerated freeze-thaw damage of MS concrete. It was thus concluded that the critical MB value of 1.4 would not cause significant deterioration in the performance of MS concretes.

Influence of MB-value of Manufactured Sand on the Shrinkage and Cracking of High Strength Concrete

The relation between methylene blue （MB） value of MS and its limestone dust content and clay content was investigated. The effects of MB value ranging from 0.35 to 2.5 on the workability of fresh concrete and crack propagation characteristics at the age of 24 hours, and effects on the mechanical properties, dry shrinkage of the harden concrete were tested. The experimental results show that the MB value is not related with the limestone dust content of MS, but in direct proportion to clay content. With the increase of MB value, the concrete workability decreases, and the flexural strength and 7 d compressive strength reduce markedly, whearas the 28 d compressive strength is not affected. When the MB-value is less than or equal to 1.35, the change of the MB-value has a little influence on early plastic cracking and dry shrinkage property of concrete, but when the MB-value is more than 1.35, the tendency of plastic cracking and dry shrinkage is remarkable.

Relationships between Modified Methylene Blue Value of Microfines in Manufactured Sand and Concrete Properties

To better understand and assess the effect of microfines on concrete properties, the synergetic effect of methylene blue value and content of microfines on properties of low and high strength concrete was studied and then the relationships between the index of modified methylene blue value （MMBV） and concrete properties were investigated. The results show that relationships between MMBV and fresh and hardened properties of concrete can be fully established, and the correlation between MMBV and C60 concrete property is higher than the correlation between MMBV and C30 concrete. With the increase of MMBV, concrete workability and frost resistance decrease while drying shrinkage decreases; however, compressive strength and chloride-ion penetration resistance of C30 concrete have not been negatively affected whereas those of C60 concrete are significantly deteriorated when MMBV exceeds 100. To make use of microfines without remarkably damaging concrete quality, it is suggested that MMBV of microfines in MS used in C30 and C60 concrete be no more than 100.

Effects of the Lithologic Character of Manufactured Sand on Properties of Concrete

Six representative parent rocks of sand, including limestone, quartzite, gneisses, granite, Basalt and Marble were selected to conduct a systematical research on the effects of various lithologies of manufactured sand on the workability, mechanism properties, volume stability and durability of manufacturedsand concrete. The experimental results show that the strength of manufactured-sand concrete is slightly higher than that of natural-sand concrete. Furthermore, substituting 15% cement of the concrete mixture with equal quantity of the six different lithology stone powder respectively, the data indicated that they can improve the concrete’s workability, postpone the plastic cracking time, enhance the anti-cracking grade, and have no obvious effect on the properties of antifreeze and sulfate attack resistance but reduce the capability to resist chloride ion penetration. Moreover, the differences in concrete’s workability, mechanism properties, volume stability and durability caused by various lithologies of manufactured sand and stone powder were not significant and the influence of lithology variety on the macro properties of concrete could be neglected eventually.

Self-compacting Concrete-filled Steel Tubes Prepared from Manufactured Sand with a High Content of Limestone Fines

To meet the requirements of construction of concretes filled in the steel tube arches,a C60 grade micro-expansive self-compacting concrete （SCC） was prepared from manufactured sand （MS）.The utilization of MS with a high content of quarry limestone fines was dealed for SCC applications.The workability,compressive and splitting strength,modulus of elasticity,restrained expansion and chloride ion permeability as well as freeze-thaw resistance of three MS-SCC mixes with fines content of 3%,7% and 10% were tested and compared with those of the natural sand （NS）-SCC mix.The experimental results indicate that the performances of the C60 MS-SCC with fines content of 7% are excellent and compared favorably with those of C60 NS-SCC.

Constraints in Using Manufactured Sands in Concrete Pavements in Australia

Due to the shortages of natural sands along the east coast of Australia in particular and the need to fully utilise fines produced in quarry operations, progress has been made in utilising blends of manufactured sands and natural sands in concrete pavements. This paper documents some of the constraints in utilising larger proportions of manufactured sands in concrete pavements. These constraints are mainly caused by the current level of knowledge regarding the impact of manufactured sands on skid and abrasion resistance of concrete pavements. This paper presents a brief review of literature on this subject in the USA, France and UK. It also briefly documents work recently carried out in Australia by CCAA （Cement Concrete and Aggregates Australia）, referring to the skid and abrasion resistance of concrete pavements using manufactured sands. The paper concludes that there is no relationship between the free silica content and the skid resistance. With regard to the abrasion resistance, it is rather the curing conditions and the compressive strength that are more important in achieving good results.

Effect of microlimestone on properties of self-consolidating concrete with manufactured sand and mineral admixture

Self-consolidating concrete(SCC)with manufactured sand(MSCC)is crucial to guarantee the quality of concrete construction technology and the associated property.The properties of MSCC with different microlimestone powder(MLS)replacements of retreated manufactured sand(TMsand)are investigated in this study.The result indicates that high-performance SCC,made using TMsand(TMSCC),achieved high workability,good mechanical properties,and durability by optimizing MLS content and adding fy ash and silica fume.In particular,the TMSCC with 12%MLS content exhibits the best workability,and the TMSCC with 4%MLS content has the highest strength in the late age,which is even better than that of SCC made with the river sand(R sand).Though MLS content slightly affects the hydration reaction of cement and mainly plays a role in the nucleation process in concrete structures compared to silica fume and fly ash,increasing MLS content can evidently have a significant impact on the early age hydration progress.TMsand with MLS content ranging from 8%to 12%may be a suitable alternative for the Rsand used in the SCC as fine aggregate.The obtained results can be used to promote the application of SCC made with manufactured sand and mineral admixtures for concrete-based infrastructure.

Effects of microfine aggregate in manufactured sand on bleeding and plastic shrinkage cracking of concrete

Construction industries have started to utilize manufactured sand(MS)as an effective alternative for river sand in concrete.High-grade parent rocks are crushed to obtain MS,which also produces a considerable amount of microfine aggregate(MFA).The higher percentage of MFA could lead to both positive and negative effects on the performance of cement-based mixes.This research was done to examine the influence of varying MFA levels,specifically 0%,3%,6%,9%,and 12%(by weight)as the partial replacements of MS on bleeding and plastic shrinkage cracking of concrete.In addition to the varying MFA levels,some concrete mixes also included fly ash(FA)and superplasticizer to investigate the effect of free-water content in the mixes.The bleeding test data were taken as on-site measurements,while the cracks from the plastic shrinkage cracking test were evaluated using an image processing technique.The results concluded that the MFA replacements and the effective water-to-cement ratio have a significant effect on the selected concrete properties.With the increasing replacement levels,cumulative bleeding and crack initiation life gradually decreased,while a progressive increase was observed for crack width,crack length,and crack area.

Suitability of marble powders in production of high strength concrete

A tremendous amount of non-biodegradable waste is created during mining and processing tasks of layered stones like marble.Over time,this has become a global problem because it harms the environment in multiple ways.Hence,it is necessary to find an alternate way to securely dispose and reuse marble wastes.The construction sector is one of the significant consumers of natural resources for the production of material binders and aggregates.As a result,in recent years,number of researchers have carried out studies in which various kinds of marble waste have been incorporated into concrete with the intention of substituting either cement or aggregates or both.This paper presents the effect of two locally sourced waste marble powders Kadapa marble powder(KMP)and Bethamcherla marble powder(BMP)as partial replacement of cement on mechanical and durability properties of high strength concrete(HSC).Their effect at different replacement levels in HSC is evaluated in compressive,indirect tensile and flexural strengths,elastic modulus,chloride penetration resistance and freeze-thaw durability properties.Micro-structural investigation is also conducted to evaluate their impact on the matrix of HSC containing waste marble powders as additional cementitious materials.Results show that the HSC consisting of KMP and BMP content of 10%and 15%,respectively exhibited higher mechanical and durability properties than the control HSC.Micro-structural investigation also supports this finding.It can be concluded that the use of marble powders as partial replacement of cement does not have any adverse impact on the properties of concrete.The use of KMP and BMP reduces the vast amount of energy required to produce cement,cost and time with reduction in environmental hazards.