Influence of Waste Rubber Powder on the Mechanical and Abrasion Resistance Properties of Concrete

Effects of pH and Mixing Agents on the Temporal Setting of Tooth-colored and Gray Mineral Trioxide Aggregate

The effects of Mg and Si additions into the matrix on the tensile, bending and compressive strengths of the carbon fiber reinforced aluminium alloys (CFRM: PAN based high modulus CF, Vf=70%) fabricated by a pressure infiltration method have been studied.The main results obtained are as follows.(1) Mg addition up to 10 mass% to the Al matrix increases the bending strength up to 1250 MPa at about 8%Mg, but decreases the compressive strength to 600 MPa. The FRM with the matrix of Al-7.8%Mg alloy having a high bending strength of 1250 MPa and a low compressive strength of 600 MPa shows pull-out of the fibers on the fracture surface by SEM observation. No precipitates are observed by high resolution TEM in the interface between the fibers and matrix.(2) Si addition of about 3% to the Al-Mg matrix makes a significant decrease in bending strength to 900 MPa and a small decrease in compressive strength to 500 MPa.(3) Si addition up to 12 mass% to Al matrix makes a small increase in bending strength to 600 MPa and a significant decrease in compressive strength to a level lower than 500 MPa.(4) Mg addition of about 1% to the Al-Si alloy matrix makes a significant increase in compressive strength up to 1000 MPa at about 7%Si, without changing of the bending strength. The FRM with the matrix of Al-7.1%Si-0.36%Mg alloy having a low bending strength of 600 MPa and a high compressive strength of 1000 MPa exhibits flat fracture like shear mode for bending test. High resolution TEM work identifies the Al4C3 precipitates on the interface.(5) Tensile strength and bending strength have a relationship based on our results using thin bending specimen. Therefore, we regarded the bending strength as the substitute of the tensile strength.

Based on the orthogonal test method, the mixture proportion design of cement-stabilized macadam (CSM) modified with rubber powder and fiber is studied. With strength and dry-shrinkage as key indices, the influence of length of polyvinyl alcohol (PVA) fiber, fiber content, particle size of rubber powder, and rubber powder content on the performance of CSM is analyzed, and the optimum mixing proportion is determined. Based on this, the modification mechanism of CSM by rubber powder and fiber is further studied from a micro perspective. The results show that the 7-day unconfined compressive strength of CSM gradually increases with the increase of fiber length. With the increase of fiber content, the compressive strength shows a trend of first increasing and then decreasing. The 7-day unconfined compressive strength of CSM gradually increases with the increase of rubber powder mesh size and linearly decreases with the increase of rubber powder content. The 28-day average dry-shrinkage coefficient of CSM shows a trend of first decreasing and then increasing with the increase of fiber length and fiber content, and gradually increasing with the increase of rubber powder mesh number and rubber powder content. Considering the strength and shrinkage characteristics, the optimum mixing parameters are 40 mesh rubber powder, 0.5 % rubber powder, 18-mm fiber length, and 1.2-kg/m3 fiber content. Scanning electron microscopy results show that there is a gap between the rubber powder and the cement matrix, and the interface between the two is discontinuous, with weak bonding, resulting in a decrease in the compressive strength of CSM. PVA fiber can improve the toughness of CSM. It has good adhesion with cement matrix. It forms a three-dimensional network support structure in the CSM mixture and can restrain water loss in the cement matrix, thus greatly improving the cracking resistance of CSM.

Tetracalcium phosphate (TetCP, Ca4(PO4)2O) reacts rapidly with polyacrylic acid (PAA). Complete reaction results in the formation of hydroxyapatite (HAp) and calcium polyacrylate. Consequently, this combination of reactants can react to form a dental cement. However, reaction occurs so rapidly that it would be difficult to achieve a homogeneous mixture of reactants suitable for use in restorations. In order to explore extending the working time, the effects of prehydrating the TetCP to form surface layers of HAp on the TetCP particles was explored. Prehydration was found to be an effective means of allowing workability. Therefore, the effects of the proportions of TetCP and PAA, with and without HAp filler, on cement properties were investigated. The extents of the reactions were investigated by X-ray diffraction analysis; the extents of PAA neutralization were studied by Fourier transform infra-red spectroscopy (FTIR); pore structures were determined by mercury intrusion porosimetry; microstructures were observed by scanning microscopy, and compressive strengths were determined. After curing for 17 days at room temperature PAA neutralization was almost complete; however, residual TetCP could be detected by X-ray diffraction and PAA by FTIR. As expected, the compressive strengths of the cements showed a dependence on the liquid (water+polymer)-to-solid (TetCP+HAp filler) used. The presence of HAp filler caused a significant decrease in compressive strength and increasing the proportion of HAp filler resulted in a decrease in the compressive strength. The characteristics of the load-deflection curves showed a dependence on the presence of HAp filler. In the absence of filler, two slopes were observed in the curves whereas a linear curve, typical of a ceramic, was observed when HAp filler was present. Mercury intrusion porosimetry (MIP) indicated the majority of the porosity was present in pores larger than 0.1 microm. Porosity increased with increasing liquid-to-solids ratio and with an increasing proportion of HAp filler at a constant liquid-to-solids ratio. Microstructural observations indicated the effect of HAp filler on increasing porosity was the result of porosity present in the filler itself. Thus, poorly consolidated HAp filler contributed to increased porosity and reduced compressive strength.

Freeze-thaw cycles have a significant negative effect on the engineering behaviour of soil in cold regions. In this study, the compressive strength of stabilized, poorly graded sandy soil used in road pavement that was subjected to different freeze-thaw cycles was studied. Samples with three different particle shapes were stabilized with a binder developed by mixing polyvinyl acetate (PVAc) and ethylene glycol monobutyl ether (EGBE). The PVAc/EGBE weight ratio was 2:1, and PVAc was added at 1%, 2%, and 3% of the dry weight of the soil, with the effect of up to ten freeze-thaw cycles evaluated. Results showed that the addition of binder decreased optimum moisture content and increased compressive strength. An increase in particle roundness results in a decrease in the magnitude of compressive strength but increases the soil composite ductility. Changing particle shape from angular to rounded resulted in a more significant decrease in compressive strength than changing from rounded to well-rounded. The decrease in compressive strength is most significant between the first and fourth freezing-thawing cycles and marginal between the fourth and tenth. The negative effect of increasing the roundness of particles is compensated by increasing binder percentages.

This study assesses the behaviour of iron-rich type F fly ash geopolymer concretes (GC) exposed to simulated sulphate, acidic, and peat environments, typical of those encountered in tropical peatlands. GC and Portland cement (PC) concrete of comparable strengths were exposed to a range of simulated solutions for 18 months, including 5 % magnesium sulphate (MgSO4), 5 % sodium sulphate (Na2SO4), 1 % and 3 % sulfuric acid (H2SO4) and peat. The GC generally outperformed PC in all conditions. The GC showed a significant increase in strength in the first year, along with enhanced durability properties. Microstructural analysis indicated a decrease in total porosity and pore size. This was attributed to continuing geopolymerization leading to the foration of additional N-A-S-H gel, which filled the pores and solidified the concrete matrix. However, compressive strength decreased at 18 months due to crack propagation caused by drying shrinkage. In Na2SO4, GC attained an 8.9 % and 6.3 % increase in compressive strength at 12 and 18 months, respectively, again attributed to ongoing geopolymerization. GC exposed to MgSO4 exhibited a significant decrease in compressive strength of approximately 11 % at 12 months and 19.8 % at 18 months, attributed to the formation of lower-strength M-A-S-H from reaction between MgSO4 and N-A-S-H gel. After 12 months GC exposed to 1 % and 3 % H2SO4 demonstrated a decrease in compressive strength of approximately 1.2 % and 4.5 %, respectively, together with 2 % and 3 % mass loss. Chemical and microstructural data confirmed this strength reduction due to the vulnerability of N-A-S-H to when exposed to H2SO4. GC exposed to peat solution exhibited a 1.25 % increase in compressive strength at 12-month, but a decrease of 11.3 % at 18-month. Microstructural analysis observed a reduction in Na+ within GC matrix, and the presence of gypsum. The reduction in pore sizes and total porosity suggested generation of zeolite crystalline material was contributing to the pore filling.

The effects of recycled rubber powder on working abilities, density and compressive strength of high strength concrete (HSC) at room temperature were studied in this paper. The characteristics of rubberized high strength concrete (RHSC) after fire was investigated by surface observation, weight loss and retained strength testing. The sieve number of rubber powder used in test is No.40 (420μm), No.60 (250µm) and No.80 (178µm), and the content of rubber powder filled in RHSC is 1%, 2%, 3% and 4% with respect to cementation material respectively. Test results show that the increase in rubber powder content reduces the concrete strength, while the decrease in compressive strength of RHSC is less than 10% when the content of rubber powder is within 2%. RHSC with small content of rubber (1%) can restrain the spalling failure of concrete under high temperature.

Modern society's growing concern for sustainability is evident in efforts to combat environmental issues like waste accumulation and resource depletion. Recycling waste materials, such as tires and seashells, into sustainable concrete aggregates is crucial for addressing these challenges. However, integrating rubber scraps into concrete can weaken its mechanical properties, with the thickness of the interface between rubbers and cement matrix increasing with higher rubber content. Researchers are exploring ways to mitigate this strength loss by incorporating additional components into rubberized cementitious materials. Similarly, seashell waste presents challenges like soil solidification and illegal dumping, further highlighting the need for innovative solutions in waste management and construction practices. This study investigates the viability of using rubber powder (at 1%, 5%, 10%, and 15%) and clamshell powder (at 5%) as partial substitutes for sand and cement in concrete. Objectives include evaluating concrete’s mechanical properties and determining the optimal rubber powder percentage in combination with clamshell powder. Concrete proportions are meticulously calculated according to mixed design, and materials are mixed in a laboratory concrete mixer. Concrete’s fresh density was determined before pouring into cube moulds with size 100mm x 100mm x 100 mm and prism moulds with size 100mm x 100mm x 500 mm for curing. Samples are cured for 7, 14, and 28 days in water, and then subjected to compression and flexural tests. Results indicate a decrease in compression strength with higher rubber powder percentages, with 15% exhibiting the lowest compression strength (25.06 MPa) and 1% the highest (39.02 MPa). Flexural testing revealed that a combination of 1% rubber powder with clamshell powder yielded optimal results (4.97MPa). In conclusion, the study suggests that the ideal proportion of rubber with 5% clamshell powder is 1%, offering insights into sustainable construction practices.

A novel way was adopted to graft zinc oxide (ZnO) with urethane-modified dimethacrylate (UDMA) in order to utilize them as reinforcing agents in resin-based dental composites. Experimental novel composites were synthesized having UDMA-grafted and nongrafted ZnO, at a concentration of 0 wt.%, 5 wt.%, and 10 wt.%. The same concentrations of ZnO were also incorporated in Filtek Z250 XT (3 M ESPE, USA). The antibacterial behavior was evaluated against Streptococcus mutans by direct-contact test at one, three, and seven days of incubation. The compressive strength and Vickers microhardness were tested as per ISO 9917 and ISO/CD6507-1, respectively. For abrasive wear resistance, mass loss and roughness average after tooth-brushing cycles of 24,000 at custom-made tooth-brushing simulator were evaluated using noncontact profilometer. Data analysis was carried out using post hoc Tucky’s test and nonparametric Kruskal–Wallis test. Direct contact test revealed that the antibacterial potential of novel and commercial composites was increased with an increase in the concentration of grafted ZnO as compared with nongrafted, whereby the potential was the highest at day seven. There was a significant decrease in compressive strength and Vickers hardness of commercial composites on addition of grafted ZnO while there was no significant difference in the strength of experimental novel composite. The abrasive wear of commercial and experimental composites was within clinical limits. Low-temperature flow-synthesis method was successfully employed to synthesize grafted and nongrafted ZnO. The UDMA-grafted ZnO can be incorporated into dental composites without decreasing their strength and these composites can be used to combat secondary caries.

Due to its numerous technical advantages as well as health benefits, sand-lime brick is increasingly used in the construction of brick walls, especially in residential buildings. Unfortunately, the occurrence of damp leads to a sharp deterioration of the technical properties of the material and the environmental conditions inside the building. Given the importance of this issue, an attempt was made to diagnose the extent of dampness variability of the main hygrothermal and strength characteristics of calcium silicate products. The study involved the basic material properties (density in dry and water-saturated conditions), moisture-related properties (capillary adsorption coefficient and sorptivity), thermal coefficients (thermal conductivity and volumetric heat capacity) as well as mechanical properties (compressive strength). This article describes diagnostic studies that were conducted to assess the extent of the effect of dampness on the strength of sand-lime products. In order to render the diagnosis more comprehensive and to include a wider range of silicate blocks available on the market, it was decided to examine three groups of silicate blocks (strength class 15, 20 and 25) obtained from three different factories. It was demonstrated that for all the examined groups dampness caused a significant decrease in compressive strength ranging from about 30% to about 40%.

In order to solve the problem of poor crack resistance and frost resistance of semi-rigid base, rubber powder and retarder were added to a semi-rigid base mixture. First, 61 mixing ratios were determined. Then, through the unconfined compressive strength, splitting strength, and other tests, the mechanical, crack, and frost resistance properties of the retarded composite semi-rigid base coarse mixture with rubber powder were studied. Finally, the macro and micro properties of the two kinds of admixture composite semi-rigid base coarse mixtures were studied by means of SEM and industrial CT. The results show that rubber powder and retarder can effectively improve the cracking and freezing resistance of the mixture. After five freeze–thaw cycle tests, the strength of the retarded composite semi-rigid base material mixed with rubber powder decreased slightly compared with the mixture without additives. It can be seen that rubber powder improved the frost resistance of the mixture. When the content of rubber powder was 1.5%, the BDR value of the mixture increased by 8.8%. With the increase of unconfined compressive strength, splitting strength, and flexural tensile strength at 28 d and 90 d, it was found that the retarder improved the middle and late strength of the mixture. When the content of retarder was 0.09%, the increase of unconfined compressive strength at 28 d reached 3.9%. The addition of rubber powder and retarder improved the distribution of internal pores, the proportion of large pores decreased, and the proportion of small pores increased. The retarder changed the morphology of hydration products, formed a dense network supporting structure, further refined the pores, and reduced the porosity of the mixture. The proportion of pores with a volume greater than 100 mm3 in the total pore volume decreased by 26.01%, and the proportion of medium pores increased by 13.07%, thereby improving the mechanical properties of the mixture.

Based on an orthogonal experimental design, this study introduces rubber powder particle size alongside rubber powder content, aggregate gradation, and cement content as factors. A total of 16 mix proportions were formulated. For each mixture, compaction tests and unconfined compressive strength (UCS) tests were conducted. Using Statistical Product and Service Solutions (SPSS) software, a multifactor variance analysis was performed to determine the influence levels of the four factors on maximum dry density and compressive strength. The optimal mix proportion was selected based on compressive strength. The results indicate that aggregate gradation and rubber powder content significantly affect the maximum dry density of the mixture, with aggregate gradation having the greatest impact. Rubber powder content has the most substantial effect on compressive strength, while rubber particle size has the least influence. The optimal formulation is 7% cement content, 30-mesh rubber powder, 0.5% rubber powder content, and a skeletal dense gradation close to the median.

The influence of limestone powder concrete on working performance and mechanical properties are researched under which it is changed substitution rate of rubber powder and mixing ratio of rubber powder with different fineness under equal substitution rate. Take C30 concrete as an example, two proportioning schemes are set respectively: The machine-made sand of limestone powder concrete is replaced by 20 mesh rubber powder equal volume; Under the specific constant volume rate of substitution, changing the mixing ratio of 20 and 40 mesh rubber powder to research working performance and mechanical properties of concrete. The results show that the substitution rate of 20 mesh rubber powder is less than 10%, increasing the slump of concrete. On the contrary, the slump of concrete decreases sharply and the flow performance weakens. The compressive strength of concrete decreases sharply when increasing substitution rate of 20 mesh rubber powder. When Increaseing the mix ratio of 20 and 40 mesh rubber powder under equal substitution rate, the slump of concrete increases and the compressive strength increases first and then decreases. Fixing the mixing ratio, the slump and compressive strength decrease with the increase of rubber powder substitution rate. When the mixing ratio of 20 and 40 mesh rubber powder is 2:1, the compressive strength of concrete is higher.

In heavily populated urban areas, high rainfall can cause inundation and even flooding because the catchment area is decreasing. To reduce rainwater runoff and increase groundwater recharge, porous concrete can be used in housing area, in parking lots and roads with low traffic loads. Porous concrete is an environmentally friendly and sustainable building material. This study aims to examine the effect of aggregate composition on the porosity and tensile strength of porous concrete. The composition of the concrete mixture is determined based on the weight ratio between portland cement type I (PC) and coarse aggregate (AK), i.e. 1 PC : 3 AK, 1 PC : 4 AK, and 1 PC : 5 AK and the ratio of fine aggregate weight (AH) of 0 ; 0.5 ; 1, and the w/c is 0.5. For each variation, six 150 mm cubes were made. The parameters tested were slump, volume weight, porosity and compressive strength at day 28. The results show that the more coarse aggregate, the lower the volume weight and its compressive strength, and the higher the porosity and slump. Fine aggregate addition increases the compressive strength and volume weight and decrease slump value and porosity. The highest slump value (205 mm) and the smallest volume weight and compressive strength were obtained from concrete mixture with PC/AK=1/5 without AH content. The smallest slump (170 mm) and porosity values were obtained from concrete mixture with PC/AK=1:3 and AH/AK=1 and the largest volume weight and compressive strength. In this study, the slump value tends to be directly proportional to porosity and inversely proportional to volume weight and compressive strength. For further research, it is recommended that the w/c value be reduced to get a larger porosity value but without a significant decrease in compressive strength.

Pervious concrete is a kind of sustainable pavement with high permeability which is becoming more common as a storm water management. The purpose of this study was to investigate the effects of coarse aggregate on physical and mechanical properties of the pervious concrete such as density, strength, porosity and permeability at 7, 28, 56 days. This experimental investigation conducted by comparing nine different mixtures. Taguchi design of experiments used to optimize the performance of these characteristics. To test the influence of aggregate systematically, water to cement ratio (w/c), paste content and coarse aggregate size were kept constant at 3 levels. 9.5, 12.5 and 19.0 mm were used for maximum aggregate sizes. The relationship between strength and porosity for pervious concrete are found to be dependent on coarse aggregate size. The test results demonstrated when the maximum size of the coarse aggregate increased, the strength decreases and the permeability and porosity grows up. An increased aggregate amount resulted in a significant decrease in compressive strength due to the subsequent decrease in paste amount. Age and coarse aggregate size had effect on the pervious concrete characteristic. To meet the specification requirements in the mix design of pervious concrete, considering both compressive strength and permeability is necessary. Finally, a parametric study is conducted to investigate the influence of design factors on the properties of porous concrete. The general equations for pervious concrete are related to compressive strength and void ratio for different aggregate sizes.