Numerical modelling of the mechanical behaviour of rubbercrete
Introduction
Concrete is often chosen in construction for its readily available raw materials, for its low cost and its durability. On the other hand, there is some concern about the sustainability of the concrete production process especially about the carbon footprint related to the use of cement and about the excessive consumption of natural aggregates.
At the same time, due to the rapid expansion of the automobile industry, large amounts of waste rubber tyres are accumulated in the world every year [1] (about 290 million in the United States and about 180 million in Europe) waiting for a way to be recycled.
In recent years, many authors have investigated on the re-use of waste tyre rubber in the construction industry, eventually in the form of artificial aggregates for concretes, as partial replacement of the natural aggregates. In this case, the resulting composite material takes the name of rubbercrete and its use allows to combine the benefits of recycling with the possibility of a significant reduction of the natural aggregate consumption related to the concrete production.
Rubber derived from cars or trucks tyres is heterogeneously composed by approximately 60% of rubber mixture, 22% of synthetic fibre and 18% of steel wire. To obtain rubber particles to be used in concrete mixtures, tyres are subjected to mechanical grinding so that crumbs and chips are obtained. Before their use in the mixture, crumbs and chips may also be subjected to chemical or natural pre-treatments and cryogenic process. Tyre rubber chips and crumbs can be used in the mixture without their textile parts and steel fibres, after treatments.
Literature studies demonstrate that concrete containing rubber aggregates has several interesting properties (sometimes very different from those of standard concrete) that encourage its use in the construction industry [2], [3], [4], [5], [6], [7]. According to Chung and Hong [8] rubbercrete usually exhibits better freeze-thaw resistance and better weathering properties compared to ordinary concrete. The replacement of natural aggregates with rubber reduces the Young elastic modulus, allowing the material to absorb energy. The high vibration damping capacity, the impact resistance and the high thermal and acoustic insulation [9] of rubbercrete allow its use for specific applications including sub-foundations, road pavements, trench filling, Jersey barriers, etc. Thanks to its reduced specific weight compared to ordinary concrete, rubbercrete also represents an interesting option for architectural applications.
On the other hand, the introduction of rubber aggregates induces reductions in the mechanical properties of the rubbercrete, in terms of compressive, tensile strength and elastic modulus, together with a reduction in workability. Since aggregates represent the major constituent of the concrete mixture, their individual properties affect the properties of the whole final mixture [10], [11], [12]. In particular, the mineralogical composition of the aggregates affects their crushing strength, hardness and elastic modulus, which in turn influence the strength and durability properties of the whole hardened concrete.
In literature, a deterioration in the concrete strength properties is observed when fine aggregates are replaced with crumb rubber [13], [14], [15]. Moreover, a greater reduction in concrete strength properties is observed when coarse aggregates are replaced with crumb rubber [16], [17], [18], [19], [20], [21]. In concrete containing rubber with a rougher surface texture, a lower reduction in strength is noticed compared to rubber aggregates which have smooth surface and spherical shape [22].
Although even tensile and bending strength decrease, a higher decrease is observed in terms of compressive strength [23], [24], [25], [26], [27], [28], [29], [30], [31].
The compressive strength decreases more when the amount of rubber introduced in the mixture increases and when substitutions are operated on coarse aggregates rather than on fine ones [16], [22], [26], [29], [32], [33].
Different reasons for strength reduction in rubbercrete mixes can be hypothesized.
First, since rubber aggregates are characterized from a very low modulus of elasticity (in the order of 2–10 MPa) compared to that of concrete (in the order of 30,000 MPa) and compared to that of natural aggregates, this discrepancy makes rubber particles similar to voids into concrete [16], [27], [34], [35]. Secondly, because rubber particles have lower strength than the concrete matrix around them, when a force is applied, cracks take place at the contact zone between the rubber particles and the concrete matrix, then gradually propagate under load until concrete crumbles [10], [16], [19], [21], [22], [23], [26], [29], [33]. The third possible reason refers to the poor adhesion between the rubber particles and the cement paste, due to the hydrophobic nature of the rubber, which contributes to further weaken the mechanical resistance of the whole mixture [13], [26], [36].
On this purpose, many authors confirmed that rubber pre-treatment might increase the compressive strength of the mixture. In Siddique and Naik [13], Güneyisi et al. [26], Li et al. [28], Papakonstantinou and Tobolski [29], Segre and Joekes [36], soaking waste tyre rubber in NaOH solution was proved to increase the rubber particles adhesion to the cementitious matrix. Even using rubber particles washed in water was found to determine a 16% increased compressive strength compared to concrete mixtures containing untreated rubber [22], [33], [29], and a further improvement (higher than 57%) was obtained with rubber aggregates treated with carbon tetrachloride [37]. On the other hand, Biel and Lee [38] reported that the cement type has an influence on the final compressive and tensile strength of the rubbercrete, in particular a better bonding was found when magnesium oxychloride cement was used.
Yilmaz and Degirmenci [39] reported that the compressive strength and the elastic modulus of rubbercrete reduced less when percentages of fly ash were introduced in the mixture. The elastic modulus decreased with increasing rubber content in a way similar to that observed with respect to the compressive strength. Schimizze et al. [40] demonstrated that the Young elastic modulus of the mix containing coarse rubber granules decreased to about 72% of that of the control mixture, whereas the mix containing the fine rubber granules showed a reduction to about 47% of that of the control mixture. The reduction in the elastic modulus indicates higher flexibility, which may be viewed as a positive gain in case of particular applications including for examples in stabilized base layers in flexible pavements. With the use of silica fume, however, the elastic modulus of the rubberised concrete slightly increased (up to 15%) although this increment was clearly noticed to be smaller in comparison to the increment in terms of compressive and splitting tensile strengths, respectively [26].
In literature a large number of micro-mechanics models have been proposed to estimate the properties of materials with defects (voids, micro-cracks, etc.) [41], [42], [43], [44], [45], [46], [47]. Also, a lot of numerical and FE models have been developed to modeling concrete and concrete structures. Buyukozturk investigated the constitutive modeling of concrete in finite element analysis [48]. Hawileh et al., instead, developed a finite element simulation of concrete beams with different kinds of reinforcement: with external short-length CFRP plates [49], with side-bonded FRP laminates [50], with a hybrid combination of steel and aramid reinforcement [51].
Although a large number of numerical models have been proposed to study modified concretes, FEM simulations on concrete with rubber aggregates from waste tyres are not found in the literature and most of the research only results from experimental investigations.
In this paper, a FE modelling was developed to describe the mechanical behaviour of rubbercrete. The effects on the compressive strength and on the elastic modulus of rubbercrete are investigated according to the different characteristics of the rubber particles, including their size, their elastic modulus and their amount (in terms of percentages of substitution of the natural aggregates with respect to the reference concrete). Results obtained through the numerical analyses well reproduce the trends indicated by the experimental data, confirming that numerical simulations represent a promising, economic, and complementary tool (in combination with usual experimental tests) to develop new concrete mixtures at the pre-qualification stage.
Section snippets
Geometrical aspects and modeling preconditions
The task of this study is to develop a numerical model, based on FE method, for concretes with partial replacement of natural aggregates with waste tyre rubber particles.
The number, the size and the spatial distribution of these rubber particles in the rubbercrete matrix are very crucial with respect of the final mechanical properties of the resulting concrete, so, in this study, these parameters have been taken into account as modelling preconditions.
In this study, FE models were developed and
Effects on the compressive strength
Predicted compressive strength values resulted from the numerical analyses are presented in Fig. 6. In this graph, the strength reduction factor (SRF), defined as the ratio among the rubbercrete compressive strength Fc and the reference concrete compressive strength Fc0, is plotted in relation to the percentage of the rubber particles with respect to the total concrete volume. The SRF is unity at 0% rubber content, representing the reference mix.
According to the plotted data, a reduction in the
Influence of the elastic modulus of the rubber (ER)
The large difference between the elastic modulus of tyre rubber particles (1.97 MPa) [35] compared to that of natural aggregates explains the reduced mechanical performances of rubbercrete compared to ordinary concrete. Although rubber particles cannot be physically assimilated to voids, it is worth to note the elastic modulus of rubber particles, which is known to be in the range of just a few MPa (0.5–2 MPa), is actually negligible compared to that of ordinary concrete (usually measuring
Future research
Our goal for future works is to investigate rubbercrete behaviour with more complex models and approaches. The use of Stochastic modelling to investigate numerical modelling of rubbercrete surely represent an interesting approach to be developed with the use of specific tools in order to implement the model. Authors are carrying on studies in which several parameters are considered to examine the performances of rubbercrete mixtures under different stress conditions, and the use of artificial
Conclusions
In this study, several FE models were developed to describe the mechanical behaviour expected from rubbercrete, which is a concrete modified by partial replacement of natural aggregates with rubber particles from recycled waste tyres.
Effects on the compressive strength and on the Young elastic modulus of the rubbercrete were investigated according to different characteristics of the rubber particles, including their size, their elastic modulus and their amount in terms of percentages of
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
References (68)
- et al.
Scrap-tyre-rubber replacement for aggregate and filler in concrete
Constr Build Mater
(May 2009) Prediction of density and compressive strength for rubberized concrete blocks
Constr Build Mater
(Nov. 2011)- et al.
Mechanical and dynamic properties of self-compacting crumb rubber modified concrete
Constr Build Mater
(Feb. 2012) - et al.
Expansion under water and drying shrinkage of rubberized concrete mixed with crumb rubber with different size
Constr Build Mater
(Apr. 2012) - et al.
Properties of concrete containing scrap-tire rubber - an overview
Waste Manag
(2004) - et al.
Cement-based materials containing shredded scrap truck tyre rubber
Constr Build Mater
(1996) The properties of rubberized concretes
Cem Concr Res
(Feb. 1995)- et al.
Collision behaviours of rubberized concrete
Cem Concr Res
(Dec. 1997) - et al.
Physico-mechanical properties of aerated cement composites containing shredded rubber waste
Cem Concr Compos
(Aug. 2006) - et al.
Tyre rubber waste recycling in self-compacting concrete
Cem Concr Res
(Apr. 2006)
Structural and mechanical studies on modified reused tyres composites
Eur Polym J
Properties of rubberized concretes containing silica fume
Cem Concr Res
Fire performance of recycled rubber-filled high-strength concrete
Cem Concr Res
Development of waste tire modified concrete
Cem Concr Res
Use of waste tire steel beads in Portland cement concrete
Cem Concr Res
Influence of scrap rubber addition to Portland I concrete composites: destructive and non-destructive testing
Compos Struct
Measurement and prediction of the strength of rubberized concrete
Cem Concr Compos
Promoting the use of crumb rubber concrete in developing countries
Waste Manag
Waste tyre rubberized concrete: Properties at fresh and hardened state
Waste Manag
Use of tire rubber particles as addition to cement paste
Cem Concr Res
Possibility of using waste tire rubber and fly ash with Portland cement as construction materials
Waste Manag
A generalized self-consistent mechanics method for composite materials with multiphase inclusions
J Mech Phys Solids
Analysis of a zig-zag array of circular holes in an infinite solid under uniaxial tension
Int J Solids Struct
The elastic moduli of a sheet containing circular holes
J Mech Phys Solids
Constitutive modeling of concrete in finite element analysis
Comput Struct
Finite element simulation of reinforced concrete beams externally strengthened with short-length CFRP plates
Compos Part B Eng
Finite element modeling of reinforced concrete beams externally strengthened in flexure with side-bonded FRP laminates
Compos Part B Eng
Finite element modeling of reinforced concrete beams with a hybrid combination of steel and aramid reinforcement
Mater Des
Simulations of FRP reinforcement in masonry panels and application to a historic facade
Eng Struct
A punching shear mechanical model for reinforced concrete flat slabs with and without shear reinforcement
Eng Struct
Impact or blast induced fire simulation of bi-directional PSC panel considering concrete confinement and spalling effect
Eng Struct
Effective elastic properties of randomly distributed void models for porous materials
Int J Mech Sci
A software framework for probabilistic sensitivity analysis for computationally expensive models
Adv Eng Softw
Permeability properties of self-compacting rubberized concretes
Constr Build Mater
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