Characterization of Mechanical Properties of Waste Slurry Modified by Recycled Sand and Cement

In order to study the modification effect of recycled sand on cement reinforced waste slurry(CWS),triaxial test,scanning electron microscope test and X-ray diffraction test were carried out.The mechanical test of recycled sand and cement reinforced waste slurry(RCWS)shows that the deviatoric stress–strain curve of RCWS samples changes from hardening type to softening type with the increase of recycled sand content;the peak stress increases with the increase of recycled sand content;recycled sand can enhance the shear strength of CWS by increasing both cohesion and internal friction angle.The microscopic test shows that recycled sand can improve the structural compactness by cementing with hydrated calcium silicate and can reduce the void ratio and orientation index of RCWS samples.Finally,the mathematical model between shear strength parameters and void ratio is established.The research shows that adding an appropriate amount of recycled sand and cement has a good modification effect on waste slurry.This is an effective method to treat two kinds of construction wastes:construction waste slurry and waste concrete.

Assessing the microbiota of recycled bedding sand on a Wisconsin dairy farm

Background:Sand is often considered the preferred bedding material for dairy cows as it is thought to have lower bacterial counts than organic bedding materials and cows bedded on sand experience fewer cases of lameness and disease.Sand can also be efficiently recycled and reused,making it cost-effective.However,some studies have suggested that the residual organic material present in recycled sand can serve as a reservoir for commensal and pathogenic bacteria,although no studies have yet characterized the total bacterial community composition.Here we sought to characterize the bacterial community composition of a Wisconsin dairy farm bedding sand recycling system and its dynamics across several stages of the recycling process during both summer and winter using 16S rRNA gene amplicon sequencing.Results:Bacterial community compositions of the sand recycling system differed by both seasons and stage.Summer samples had higher richness and distinct community compositions,relative to winter samples.In both summer and winter samples,the diversity of recycled sand decreased with time drying in the recycling room.Compositionally,summer sand 14 d post-recycling was enriched in operational taxonomic units(OTUs)belonging to the genera Acinetobacter and Pseudomonas,relative to freshly washed sand and sand from cow pens.In contrast,no OTUs were found to be enriched in winter sand.The sand recycling system contained an overall core microbiota of 141 OTUs representing 68.45%±10.33%SD of the total bacterial relative abundance at each sampled stage.The 4 most abundant genera in this core microbiota included Acinetobacter,Psychrobacter,Corynebacterium,and Pseudomonas.Acinetobacter was present in greater abundance in summer samples,whereas Psychrobacter and Corynebacterium had higher relative abundances in winter samples.Pseudomonas had consistent relative abundances across both seasons.Conclusions:These findings highlight the potential of recycled bedding sand as a bacterial reservoir that warrants further study.

Basic Properties of Concrete Incorporating Recycled Ceramic Aggregate and Ultra-fine Sand

Recycled ceramic mixed sand（RCMS） was obtained by partially replacing ultra-fine sand with recycled ceramic coarse sand（RCCS）. The effects of RCCS replacement rate on the apparent density, workability, compressive strength and splitting tensile strength of recycled ceramic concrete（RCC） were investigated. In addition, the relationship between the water-cement ratio and compressive strength of RCC was also studied. The experimental results indicate that the reusing of recycled ceramic aggregate can improve the cohesiveness and water retentiveness of fresh concrete and benefit the mechanical properties development. When the RCCS replacement rate is not less than 40%, the mechanical properties of RCC are superior to those of the reference concrete. Moreover, when recycled ceramic medium sand was completely used as fine aggregate, the maximum increase in both compressive strength and splitting tensile strength were obtained, comparing with those of reference concrete, the increment ratio was 19.85% and 32.73%, respectively. The microscopic analysis shows that the using of recycled ceramic aggregate can meliorate distinctly the structure of the interfacial transition zone（ITZ） and increase the compaction degree of cement paste. Furthermore, an expression of the compressive strength of RCC and the cement-water ratio is regressed and gains a good linear relativity. It is an effective way to recycle waste ceramic, and the consumption of recycled ceramic aggregate could reach from 26.9% to 47.6% of the total weight of aggregate in producing concrete.

Effects of coarse and fine aggregates on long-term mechanical properties of sea sand recycled aggregate concrete

Typical effects of coarse and fine aggregates on the long-term properties of sea sand recycled aggregate concrete(SSRAC)are analyzed by a series of axial compression tests.Two different types of fine(coarse)aggregates are considered:sea sand and river sand(natural and recycled coarse aggregates).Variations in SSRAC properties at different ages are investigated.A novel test system is developed via axial compression experiments and the digital image correlation method to obtain the deformation field and crack development of concrete.Supportive results show that the compressive strength of SSRAC increase with decreasing recycled coarse aggregate replacement percentage and increasing sea sand chloride ion content.The elastic modulus of SSRAC increases with age.However,the Poisson’s ratio reduces after 2 years.Typical axial stress-strain curves of SSRAC vary with age.Generally,the effect of coarse aggregates on the axial deformation of SSRAC is clear;however,the deformation differences between coarse aggregate and cement mortar reduce by adopting sea sand.The aggregate type changes the crack characteristics and propagation of SSRAC.Finally,an analytical expression is suggested to construct the long-term stress-strain curve of SSRAC.