Mechanical Properties of Self-Compacting Rubberized Concrete with Different Rubber Types under Triaxial Compression

Different rubber aggregates lead to changes in the effect of stress conditions on the mechanical behavior of concrete,and studies on the triaxial properties of self-compacting rubber concrete(SCRC)are rare.In this study,35 cylindrical specimens taking lateral stress and rubber type as variables were prepared to study the fresh properties and mechanical behaviors of SCRC under triaxial compression,where the rubber contains two types,i.e.,380μm rubber powder and 1–4 mm rubber particles,and four contents,i.e.,10%,20%and 30%.The test results demonstrated that SCRC exhibited a typical oblique shear failure mode under triaxial compression and had a more moderate descending branch compared with self-compacting concrete(SCC).The presence of lateral stress can significantly improve the compression properties,including initial elastic modulus,peak stress and peak strain,with an improvement range of 3%–73%for peak stress.While rubber aggregates mainly targeted the deformation abilities and toughness for improvement,and the peak strain improvement ranges were 0.1–3.1 times and 0.1–1.0 times for SCRC containing rubber powder and SCRC containing rubber particles,respectively,relative to SCC.At a high lateral stress of at least 12 MPa,the loss of strength due to the addition of rubber can be controlled within 10%,in which case the content of rubber powder and rubber particles was recommended to be at most 20%and 30%,respectively.Based on the Mohr-Coulomb theory,the failure criteria of SCRC with different rubber types were established.For analysis and design purposes,an empirical model was proposed to predict the stressstrain behavior under triaxial compression,considering the influence of different rubber content and lateral stress.The results obtained in this study can provide a valuable reference for the design and application of self-compacting rubberized concrete in practical projects,especially those involving three-way compression states and requiring high-quality deformation and energy dissipation.

Effect of Rubber Particle Modifi cation on Properties of Rubberized Concrete

To improve the combination of cement matrix and waste tire rubber particles in concrete, the rubber particles were treated with acrylic acid（ACA） and polyethylene glycol（PEG） for grafting hydrophilic groups on their surfaces. The X-Ray photoelectron spectroscopy（XPS） and surface contact angle were used to characterize the hydrophilicity and surface functional group of rubber particles. The effect of rubber particle modifi cation on fresh/hardened properties of rubberized concrete was studied. The experimental results show that the contact angle between rubber particle surface and water decreases when rubber particle is modifi ed. Compared with the unmodifi ed rubberized concrete（RC）, the unit weight of modifi ed rubberized concrete（MRC） changes slightly. However, the slump, air-entrainment, compressive strength, flexural strength, and impact performance of MRC are obviously improved. Under good condition of slump, the water-cement ratio of the MRC can be reduced from 0.4 to 0.38. And the compressive strength and fl exural strength of the MRC（10% rubber particle content） can be increased by 25.9% and 26.4%, respectively.

The Abrasion-resistance Investigation of Rubberized Concrete

The abrasion resistance properties of rubberized concrete were comparatively studied by taking silica fume and crumb tire rubber as the additives. The abrasion tests were conducted in accordance with the Chinese standard test method DL/T 5150 - 2001, two recommended test methods： under water method and ring method, were used. The crumb tire rubbers with the sieve size of 8-mesh and 16-mesh were incorporated into the concrete by replacing same volume of sand and as an additive. The abrasion resistance of concrete was evaluated according to the abrasion resistance strength and the mass loss. Test results show that the addition of silica fume enhanced both compressive strength and abrasion resistance of concrete, and the addition of crumb rubber reduced the compressive strength but increased notably the abrasion resistance of the concrete. Silica fume concrete performed a better abrasion resistance than control concrete, and the rubberized concrete performed a much better abrasion resistance than silica fume concrete. The abrasion resistance of rubberized concrete increased with the increase of rubber content.

Acoustic emission characteristics of damage evolution of multi-scale fiber reinforced rubberized concrete under uniaxial compression and tension after being subjected to high temperatures

Recently developed multi-scale fiber(i.e.,CaCO3 whisker,polyvinyl alcohol(PVA)fiber,and steel fiber)reinforced rubberized concrete exhibits excellent mechanical properties and spalling resistance at high temperatures.Measurement of macro properties such as strength and Young’s modulus cannot reveal and characterize damage mechanisms,particularly those relating to the multi-scale fiber strengthening effect.In this study,acoustic emission(AE)technology is applied to investigate the impact of multi-scale fiber on the damage evolution of rubberized concrete exposed to high temperatures,under the uniaxial compression and tension loading processes.The mechanical properties,AE event location,peak frequency,b-value,the ratio of rise time to amplitude(RA),average frequency(AF)values,and AE energy of specimens are investigated.The results show that the number of events observed using AE gradually increases as the loading progresses.The crumb rubber and fibers inhibit the generation and development of the cracks.It is concluded that both the peak frequency and b-value reflect the extension process of cracks.As the cracks develop from the micro scale to the macro scale,the peak frequency tends to be distributed in a lower frequency range,and the b-value decreases gradually.At the peak stress point,the AE energy increases rapidly and the b-value decreases.The specimens without multi-scale fibers exhibit brittle failure,while the specimens with fibers exhibit ductile failure.In addition,adding multi-scale fibers and crumb rubber increases the peak frequency in the medium and high frequency ranges,indicating a positive effect on inhibiting crack development.After being subjected to high temperatures,the maximum and minimum b-values decrease,reflecting an increase in the number of initial cracks due to thermal damage.Meanwhile,the RA and AF values are used to classify tensile and shear cracks.The specimens fracture with more shear cracks under compression,and there are more tensile cracks in specimens with multi-scale fibers under tension.

Experimental Study of Rubberized Asphalt Emulsion Modified Portland cement concrete

The poor fatigue properties and high rigidity of cement asphalt emulsion treated mis(CETM) have for a long time been problems restricting its further development making it impossible for C-ETMto be used as surface layer materials. In this paper, a new kind of cement asphalt emulsion composite-rubberized asphalt emulsion modified Portland cement concrete (RACC) was proposed, which was formed by dispersing rubberized aSPhalt emulsion coated coarse aggregates into cement mortar matrix. In order to evaluate systematically the performance of RACC, laboratory tests with nearly one thousand SPecimen were conducted for resilient modulus, fatigue properties, ultimate ban and length,abrasion, temperature contraction, and dry shrinkage. The experimental results show that the problems existed in C-ETM have to a great extends been solved by RACc. To verify the field performance and inquire into paving technology, teSt road appearsatlsfactory it is concluded that when thed ape surface laycr of semi-rigid base course, RACC is more for surface layer material than both Portland cement concrete(PCC) and asphalt concrete(AC)

Mechanical Test and Meso-Model Numerical Study of Composite Rubber Concrete under Salt-Freezing Cycle

A composite rubber concrete(CRC)was designed by combining waste tire rubber particles with particle sizes of 3~5 mm,1~3 mm and 20 mesh.Taking the rubber content of different particle sizes as the influencing factors,the range and variance analysis of the mechanical and impermeability properties of CRC was carried out by orthogonal test.Through analysis,it is concluded that the optimal proportion of 3~5 mm,1~3 mm,and 20 mesh particle size composite rubber is 1:2.5:5.5 kinds of CRC and 3 kinds of ordinary single-mixed rubber concrete(RC)with a total content of 10%~20%were designed under this ratio,and the salt-freezing cycle test was carried out with a concentration of 5%Na 2 SO4 solution.The physical and mechanical damage laws during 120 salt-freezing cycles are obtained,and the corresponding damage prediction model is established according to the experimental data.The results show that:on the one hand,the composite rubber in CRC produces a more uniform“graded”structure,forms a retractable particle group,and reduces the loss of mechanical properties of CRC.On the other hand,colloidal particles with different particle sizes are used as air entraining agent to improve the pore structure of concrete and introduce evenly dispersed bubbles,which fundamentally improves the durability of concrete.Under the experimental conditions,the CRC performance is the best when the overall content of composite rubber is 15%.

Workability and Durability of Concrete Incorporating Waste Tire Rubber:A Review

Environmental problems caused by waste tires are becoming increasingly prominent.There is an urgent need to find a green way to dispose of waste tires,and scholars have made considerable efforts in this regard.In the construction industry,rubber extracted from waste tires can be added to concrete to alleviate environmental problems to a certain extent.As a new building material,rubber concrete has superior properties compared to ordinary concrete and has been widely used in many fields.Numerous studies have been conducted worldwide to investigate the effect of waste tire rubber on the performance of concrete.It has been reported that the addition of waste tire rubber has a significant influence on the performance of concrete.Workability influences the hardened performance of rubber concrete,especially the durability.Based on the current research results,the workability and durability of concrete manufactured with waste tire rubber,including water absorption and permeability,carbonation resistance,chloride ion permeability resistance,and freeze-thaw resistance,are summarized in this paper.It is concluded that the addition of waste tires has a negative effect on the workability of concrete.In terms of durability,concrete exhibits better chloride ion penetration resistance and frost resistance,with a higher water absorption rate,and lower anti-permeability and carbonation resistance owing to the addition of waste tire rubber.

Experimental Study and Failure Criterion Analysis of Rubber Fibre Reinforced Concrete under Biaxial Compression-Compression

In order to examine the biaxial compression-compression properties of rubber fibre reinforced concrete(RFRC),an experimental study on RFRC under different lateral compressive stresses was carried out by considering different rubber replacement rates and polypropylene fibre contents.The failure modes and mechanical property parameters of different RFRC working conditions were obtained from the experiment to explore the effects of rubber replacement rate and polypropylene fibre content on the biaxial compression-compression properties of RFRC.The following conclusions were drawn.Under the influence of lateral compressive stress,the biaxial compression-compression failure mode gradually developed from a columnar pattern to a flaky pattern,suggesting that the incorporation of rubber and polypropylene fibres into the concrete resulted in a significant change in the development of cracks.For different rubber replacement rates and polypropylene fibre contents,the vertical compressive stress exhibited the same developing trend under the influence of lateral compressive stress.Specifically,the lateral compressive stress imposed the minimum effect on the vertical compressive stress when the rubber replacement rate and polypropylene fibre content were 20%and 0.4%,respectively,and imposed the maximum effect when the rubber replacement rate and polypropylene fibre content were 20%and 0%,respectively.With the increase of rubber replacement rate,the vertical peak stress was significantly reduced,which implies that an appropriate amount of polypropylene fibres can increase the vertical peak stress to a certain extent.Then,the biaxial compression-compression mechanism of RFRC was analysed from the microscopic level by using scanning electron microscope(SEM).Meanwhile,based on Kupfer’s biaxial compression-compression failure criterion and the octahedral stress space,a biaxial compression-compression failure criterion for RFRC was proposed,which was proven to have good applicability.The research results of this study provide important theoretical basis for the engineering application and development of RFRC.

The Properties of Sulfur Rubber Concrete (SRC)

The mix designs and specimen preparation for the dry process and wet process of sulfur rubber conerete （ SRC ） were investigated. The compressive strength, corrosion-resistance and toughness were studied and discussed. The results show that SRC is corrosion-resistanet. Although the compressive strength of SRC decreases with inereasing rubber content, the toughness increases instead . Adding micro-filler will improve the compressive strength of SRC . There is a threshold value for the sulfur content, at which the compressive strength and the workability of SRC reach an optimum balance . The bond between rubber particles and surrounding sulfur is strong due to the vulcanization process that generates cross-link through S-C bonds.

Experimental Survey on Dry Asphalt Rubber Concrete for Sub-ballast Layers

This paper presents the results of an experimental survey on the potential application of DARC （dry asphalt rubber concrete） in rail superstructure, within sub-ballast layers by measuring its damping and mechanical properties. Based on the environmental friendly point of view the DARC has the significant advantage as the backfill material of sub-ballast layer because the rubber comes from the waste tires of truck and its usage can results a significant recycling of non-biodegradable wastes. After a preliminary mix-design of several DARCs, with different rubber content that confirmed by using the Marshall test, the stiffness modulus and damping ratio both of a standard bituminous mixture and of dry asphalt rubber concrete with a rubber content equal to 1.5% were determined using the four points bending device. The experimental results were compared and a numerical analysis by means of a 2D lumped mass model was developed in order to evaluate the different performance within the rail superstructure in terms both of the deflection and of the pressure on sub-grade. Both the results on the mechanical and dissipative properties of the DARC and the mechanical behavior of the correlate rail superstructure encourage the authors to continue the research on the application of such material for sub-ballast layers.

Improvement of Cracking-resistance and Flexural Behavior of Cement-based Materials by Addition of Rubber Particles

By ring test and bend test, the improvement of waste tire rubber particles on the crack- resistance and flexural behaviors of cement-based materials were investigated. Test results show that the cracking time of the ring specimens can be retarded by the incorporation of rubber particles in the cement paste and mortar. The improvement in the crack-resistance depended on the rubber fraction. When the rubber fraction was 20% in volume, the cracking time was retarded about 15 h for the paste and 24 d for the mortar respectively. Flexural properties were evaluated based on the bend test results for both mortar and concrete containing different amount of rubber particles. Test results show that rubberized mortar and concrete specimens exhibit ductile failure and significant deformation before fracture. The ultimate deformations of both mortar and concrete specimen increase more than 2-4 times than control specimens.

Material development for a sustainable precast concrete block pavement

Portland cement concrete （PCC） and asphalt concrete （AC） are the most common roadway and highway construction materials which are more suitable for continuous slab pave- ments. The durability of these materials is highly dependent on construction quality and techniques, and both materials are difficult to repair. Heavy rain storms in India have recently revealed several roadway pavement failures and resulted in significant repair costs. Interlocking block type pavements are simpler to construct and maintain than both PCC and AC pavements but, have only been used for slower traffic roads due to weak interlocking at the joints. To improve the quality of block pavements, blocks made of PCC with waste tire crumb rubber partially replacing river sand （fine aggregate） are suggested. The joint interlocks can be further improved by modifying the block geometry. The material is completely recycled and is deemed more superior than concrete pavements when repair and construction techniques and costs are concerned. This paper presents the material characterization of Rubberized Concrete Blocks （RCBs） using crumb rubber particle size ranging from 0.075 mm to 4.75 mm to partially replace the fine aggregates. It also discusses the advantages of RCB over continuous material pavements.

Seismic performance of composite moment-resisting frames achieved with sustainable CFST members

The main objective of the research presented in this paper is to study the bending behaviour of Concrete Filled Steel Tube （CFST） columns made with Rubberized Concrete （RuC）, and to assess the seismic performance of moment-resisting frames with these structural members. The paper describes an experimental campaign where a total of 36 specimens were tested, resorting to a novel testing setup, aimed at reducing both the preparation time and cost of the test specimens. Different geometrical and material parameters were considered, namely cross-section type, cross-section slenderness, aggregate replacement ratio, axial load level and lateral loading type. The members were tested under both monotonic and cyclic lateral loading, with different levels of applied axial loading. The test results show that the bending behaviour of CFST elements is highly dependent on the steel tube properties and that the type of infill does not have a significant influence on the flexural behaviour of the member. It is also found that Eurocode 4 is conservative in predicting the flexural capacity of the tested specimens. Additionally, it was found that the seismic design of composite moment- resisting frames with CFST columns, according to Eurocode 8, not only leads to lighter design solutions but also to enhanced seismic performance in comparison to steel frames.

Caltrans use of scrap tires in asphalt rubber products:a comprehensive review

The California Department of Transportation （Caltrans） has been using scrap tire rubber in asphalt pavements since the 1970s in chip seals and the 1980s in rubberized hot mix asphalt（RHMA）. Both the wet （field blend） and dry processes were used in early trials. Caltrans has also used rubber modified binders containing both crumb rubber modifier and polymer modifier that could be manufactured at a refinery facility, a terminal blend wet process. Since the beginning of this century, Caltrans increased the use of scrap tire rubber in paving projects and invested considerable resources in developing technically sound, cost effective, and environmentally friendly strategies for using scrap tire rubber in roadway applications. By the end of year 2010, approximately 31% of all hot mix asphalt （HMA） placed by Caltrans was rubberized HMA, roughly 1.2 million tons. Caltrans efforts in using asphalt rubber products were also demonstrated in its research and technology development. These included the construction of two full-scale field experiments, five warranty projects, and an accelerated pavement study using a heavy vehicle simulator. Additionally, terminal blend asphalt rubber and rubberized warm mix asphalts began to be experimented on trial basis. This paper provides a comprehensive review of Caltrans experience over four decades with asphalt rubber products. Current practices and future outlook are also discussed.