Cement-treated Base Materials Research Articles

Micromechanical Modeling of Cement-Treated Base Materials Considering Recycled Crushed Aggregate Morphology from Construction and Demolition Waste Using Three-Dimensional Discrete Element Method

Abstract This study established a three-dimensional discrete element method (3D DEM) of cement-treated base materials (CTBM), considering the morphology of recycled crushed aggregates (RCAs) derived from construction and demolition waste. Coarse RCA morphology was obtained using X-ray computed tomography and integrated into the DEM model. The linear contact model and linear parallel bond model were selected and key microparameters were determined. The developed 3D DEM model was verified through the actual indirect tensile test of CTBM. Micromechanical analysis, encompassing contact force and displacement fields of particles, was subsequently evaluated based on the virtual uniaxial compression test. The findings revealed that particles near the loading plate exhibited relatively higher contact force, gradually decreasing with distance from the loading position. Regarding the displacement field, the particles closer to the edge of the cross-section and the loading plate on the longitudinal section experienced greater displacement, whereas those in the middle of the specimen and farther from the loading plate had smaller displacements. Furthermore, it was observed that increasing the cement content effectively enhanced the internal contact force and the ability of CTBM to resist uniaxial deformation.

Application of the use of local natural materials as cement treated base materials

The use of local natural materials as alternative materials in road construction could save construction costs, especially for Maluku Province. One of the local natural materials in Maluku Province is Limestone in Kelan Village and Kaliobar Village. Therefore, this study aims to see how far the use of limestone to be applied as a cement treated base material. Before being applied, the limestone is tested first in the laboratory. After the limestone was applied as a cement treated base (CTB) material, compaction and compressive strength tests were carried out. The number of CTB compressive strength test specimens was 26 samples from STA 4+100 to STA 8+900. The limestone on Larat Island is unique in that it contains the composition CaCO3 (Calcium Carbonate), which is the result of shallow sea sedimentation. The potential of limestone in the work location area has not been utilized optimally to improve the economic level of the community. The test results show that the compressive strength values obtained are still within the interval range, namely between 25 - 40 gr/cm2. Therefore, it can be concluded that the CTB mixture material at this location meets the requirements to be used as a foundation layer for road pavement using local natural materials.

Predicting fatigue damage growth in cement-treated base layer built with construction and demolition waste

Fatigue damages of cement-treated construction and demolition waste (CDW) aggregate base materials were predicted using a nonlinear elastic-damage model coupled with a finite element (FE) program. CDW with two different gradations (BC1 and BC2) and one control cement-treated base material using quarried aggregate (N1) were tested. Three-point bending strength and fatigue tests were conducted to obtain the fracture property of the three base materials and inputs of the proposed nonlinear elastic-damage model. Pavement structures with the three base layers were modelled by FE simulations, to evaluate the mechanical and cracking performance under three different vehicle load levels of 700 kPa, 840 kPa and 1050 kPa, respectively. The result of experiments shows that the BC1 with a skeleton-dense gradation has the highest fracture strength, which was followed by the N1, and is much higher than the BC2. In the FE simulations, the proposed nonlinear elastic-damage model can well reflect the damage evolution and modulus distribution of cement-treated base layers under vehicle loading. With the accumulation of vehicle loading cycles, the damage of base layers increases, and pavement structure with the BC2 base layer shows the fastest damage evolution. Besides, the stress-dependent modulus shows a non-uniform distribution in the base layers, presenting very high values at the surface and bottom of the base layer due to the high compressive stress and tensile stresses.

Micromechanical behavior of cement-treated base materials incorporating recycled crushed aggregates arising from C&D waste powder based on DEM

A numerical simulation of the uniaxial compression test (UCT) was conducted based on the discrete element method (DEM), to investigate the mechanical properties of CTBM incorporating recycled crushed aggregates (RCAs) arising from construction waste powder. The components of CTBM were generated via the randomization method to obtain a 2D DEM model. Then, the Linearcbond Model and Linearpbond Model were selected, and the effects of the main micro-parameters of contact models on the stress–strain curves of CTBM were clarified. The final micro-parameters were determined through the trial and error method and inversion analysis. Moreover, the micromechanical results presented that the contact forces between particles during the whole loading process increased continuously until damage occurred. And the contacts between particles failed at the middle and later loading stages, especially the tension contacts. The contact number of the Linearcbond Model reduced significantly, while that of the Linearpbond Model only decreased by 2.6%. Furthermore, the upper and lower particles moved to the mid-span of the specimens, and the particles in the middle moved to both sides when loading. The displacement on both sides was larger due to the failure of the specimen in the middle and later loading periods. The presented 2D DEM has the potential to display the mechanical characteristics of CTBM. It also provides theoretical guidance for the wide application of RCAs due to their great economic and environmental benefits.

Numerical simulation of mesoscopic cracking of cement-treated base material based on random polygon aggregate model

Numerical simulation of mesoscopic cracking of cement-treated base material based on random polygon aggregate model

Utilization of RCAs arising from excavated soil in CTBM: Laboratory characterization and environmental impact assessment

A large amount of excavated soil is generated due to rapid urban infrastructure development, resulting in serious safety and environmental threats. From the perspective of resource recycling, this paper conducted a laboratory characterization and environmental impact assessment of the utilization of recycled crushed aggregates (RCAs) arising from excavated soil in cement-treated base materials (CTBM). SEM-EDS was employed to test the chemical elements and surface properties, and it reflected larger pores and cracks compared to diabase and limestone aggregates. A series of experimental tests were carried out to investigate the mechanical behaviors of CTBM with varying cement content incorporating RCAs. The laboratory test results revealed that the UCS, IDT strength, FTS and CRM increased with increasing cement content. Moreover, an environmental impact assessment of the recycling of RCAs to produce CTBM was preliminarily analyzed compared to the traditional CTBM with natural stone aggregates (NSAs). The results showed that the attenuation in different environmental impact categories was more than 26% when recycling RCAs from excavated soil to replace NSAs. It was clear that the utilization of 1 t RCAs could result in a reduction of approximately 75 MJ in energy and 5.17 kg CO2-eq in emissions just in terms of reducing transportation and landfill. Thus, a total reduction of 3.15 billion MJ energy and 21.72 million t CO2-eq emissions could be realized if all the excavated soil generated in Shenzhen annually was recycled. Furthermore, possible policies and further prospects were suggested based on the research for more sustainable management of construction and demolition waste (CDW) containing excavated soil.

Accelerating Mixture Design for Cement Treated Base Material

The stabilization of roadway and stockpile materials enhances the strength and stiffness properties of pavement base layers, allowing those layers to meet structural requirements in a cost-effective and sustainable manner. Historically, mixture stabilization design criteria have relied on unconfined compressive strength (UCS) results and, depending on the treatment type and test methods, they can take nearly a month to complete. Additionally, different treatment types currently require different preparation, curing time, and acceptance criteria. This research develops a harmonized and accelerated design procedure for cement-treated base materials with the objective of producing acceptable mixture design recommendations. This work focuses on a rapid test turnaround time, the inclusion of moisture conditioning in the mix design, and performance-related design criteria by relating an accelerated-cure indirect tensile test (IDT) to UCS and modulus of rupture (MoR). The resulting strength relationship model for the MoR, UCS, and IDT was found to show promise for estimating UCS based on an accelerated-cure IDT, and potentially estimating MoR from that same IDT. The newly formulated IDT test method illustrates the possibility of accelerating the mixture design procedure for cement-treated bases and harmonizing with mix design procedures used for emulsion and foamed asphalt-treated base materials.

Characterisation of road base materials treated by hybrid alkali-activated binders and cationic asphalt emulsions

ABSTRACT Using suitable chemically stabilized materials to solve the moisture-related damages on the road pavement is still essential. This study investigated the influence of cationic asphalt emulsion (CAE) on a hybrid alkali-activated binder (HAB) consisting of fly ash, hydrated lime, and solid sodium hydroxide for the chemically stabilized road base material. Adding CAE to HAB would introduce the water-repellent and elastic properties of HAB. Crushed rock (CR) treated with HAB binder prepared with two concentrations of CAE (HAB-CAEs) was characterized using a test series of compaction, unconfined compressive strength, resilient modulus, and water absorption. The compaction test results showed that CAE could decrease the optimum water content and air voids at the maximum dry density. Using CAE increased the strength of the HAB-CAE-treated CR, resulting in a sufficient compressive strength of the flexible pavement base. In addition, the HAB-CAE-treated CR had a proficient energy absorption under a static loading condition. The addition of CAE to the HAB-treated CR also provided resilient modulus and stiffness values higher than those of the conventional cement-treated base material with less water absorption. Therefore, HAB-CAE could be a viable option as a sustainable pavement base material.

Evaluation of fatigue performance of cement-treated composites based on residual strength through discrete element method

Fatigue damage is the process of material fatigue failure caused by cyclic loading, and the development of damage degrades the material properties. This paper aims to investigate the fatigue degradation law of cement-treated base (CTB) materials using a discrete element method (DEM) simulation technique. A fatigue evolution model was adopted to characterize the time-dependent fatigue damage under cyclic loading. Virtual semi-circular bending (SCB) fatigue and residual strength tests at different fatigue stages were performed on mesoscale DEM model to evaluate the fatigue damage of CTB material. With residual strength variable, the fatigue damage model was established to reveal the accumulation of damage. The results show that the residual strength evolution nearly appears an exponential correlation with the fatigue stages. In the first stage, the strength degradation is stable and appears as approximately linear. At about 80% of the fatigue life, the degradation rate is significantly accelerated. The residual strength degradation rate is related to the initial stress level and decreases with the increase of stress ratio. At the same fatigue life stage, the greater residual strength attenuation will be generated with a lower load level. The fatigue damage evolution model indicates the fatigue damage accumulation approximately linearly in the early stage and rapidly in the late stage. The late fatigue stage has the main contribution to fatigue failure. The degradation law demonstrates the lower the load level is, the more the damage accumulation at the same fatigue life stage will be, and the corresponding critical damage is greater. Moreover, based on the strength degradation law, a prediction model is established to evaluate the residual fatigue life of pavement base material.

Effects of pre-cracking on the early-age mechanical properties of a cement-treated base material mixed and tested in laboratory

In this paper, the effects of pre-cracking on the early-age mechanical properties of a cement-treated base material (CTBM) were studied. To do so, CTBM with 4% cement by mass of dry granular material were mixed in laboratory in order to make cylindrical specimens. Half of the specimens were pre-cracked (PC) with a mechanical impact hammer after a two days moist curing process. The immediate effect of the pre-cracking (PC) was evaluated with dynamic Young’s modulus measurements performed just before (B) and right after (A) the PC. Then, tests were performed in laboratory to compare the early-age mechanical properties (dynamic Young’s modulus, compressive and indirect tensile strengths) of the specimens without pre-cracking (WPC) and with pre-cracking (PC). As early as five days after the pre-cracking, the dynamic Young’s modulus, and the compressive and indirect tensile strengths of the PC specimens are higher than those of the WPC specimens. In addition, the pre-cracking seems to accelerate the hydration process and water evaporation. The results of this study therefore suggest that the pre-cracking only has a positive effect on the early increase of the mechanical strengths.

Meso-cracking characteristics of rubberized cement-stabilized aggregate by discrete element method

As a sustainable solution, embedding rubber inclusions in the semi-rigid pavement base course can ensure the consumption of a large amount of waste tire pollution and improve the mechanical properties of cement-treated base materials. The rubber modification has a potential effect on reducing the possibility of pavement reflective cracks caused by base cracking. This paper aims to investigate the meso-cracking characteristics of rubberized cement-stabilized aggregate (RCSA) mixtures and to quantitatively evaluate the influence of rubber inclusion content and particle size through numerical simulation. The rubber particle size of 0.6–4.75 mm was selected. The virtual RCSA samples were prepared by replacing similar-size aggregates with rubber particles based on the reference mixtures without rubber. Five volumetric replacement contents (20%, 40%, 60%, 80% and 100%) of three gradation ranges (0.6–1.18 mm, 1.18–2.36 mm, and 2.36–4.75 mm) were adopted. An indirect diametric tensile (IDT) simulation test was adopted to obtain the investigated performance of IDT strength, static stiffness, toughness and toughness index. The simulation results show that the incorporation of rubber inclusion has a negative effect on the IDT strength of the RCSA sample. However, material extensibility and post-peak toughness are improved and stiffness is reduced with increasing rubber replacement percentage. The optimal rubber content of the investigated mixtures should be controlled within 80% of the corresponding aggregate gradation volume, which is conducive to controlling the reduction of the overall strength and the play of the extensibility. The strength reduction and ductility improvement of modified concrete are positively correlated with the particle size of rubber inclusion. The modified RCSA mixture with a smaller rubber particle size could ensure a higher IDT strength and extensibility. For the investigated sample, the best comprehensive modification effect can be obtained using the finer rubber substitute with a particle size of 0.6–1.18 mm. The rubber inclusion acts similarly to a cavity defect, which will result in fracture preferring to occur adjacent to the rubber aggregate. Ignoring the adverse effect of strength, the practical implication of rubber incorporation is to improve the ductile behaviour of the RCSA mixture and reduce base cracking. The present numerical simulation methods have the potential to investigate the meso-cracking mechanism of RCSA. It also provides a theoretical guidance for the gradation design of rubberized mixtures.

Fatigue damage numerical simulation of cement-treated base materials by discrete element method

Fatigue failure of the cement-treated base (CTB) is always paid more attention by highway constructors. Meso-scale cracking evolution plays an essential role in the research of fatigue deterioration mechanism, which is hard to be characterized using experimental techniques alone. The objective of this paper is to investigate the fatigue behaviour of CTB materials under cyclic loading through the discrete element method (DEM). A parallel bond evolution model (PBEM) was developed to simulate the time-dependent fatigue damage. Integrated with the PBEM, a fatigue damage evolution model (FDEM) was established and implemented in the Particle Flow Code (PFC5.0) to describe the fatigue decay behaviour under cyclic loading. The fatigue modelling parameters were further calibrated by the notched semicircular bending (NSCB) strength and fatigue test. Then a series of virtual NSCB fatigue tests were conducted to study the decay law of CTB materials. The simulation results indicate that the fatigue damage accumulates in a nonlinear manner under cyclic loading and the steady crack growth is the main stage of fatigue failure. With the increase of stress ratio, the stable crack growth stage is shortened obviously. The established PBEM is capable of capturing the fatigue behaviour and cracking process of CTB materials. It provides a reliable numerical technique for modelling and investigating fatigue damage of cement-treated base materials.

Influence of mesoscale heterogeneous and initial defects on the fracture of cement-treated base materials

To investigate the mesoscopic fracture of heterogeneous cement-treated base (CTB) materials, a mesoscale numerical model was established through discrete element method (DEM) and randomization algorithm. The proposed model was composed of aggregate, mortar, interface transition zone (ITZ), pores and initial defects. Combined with nano-indentation test, a half-normal distribution function was used to characterize the micromechanical heterogeneity of mortar and ITZ. A discrete fracture network (DFN) was used to characterize the initial microscopic defects in mortar hardening. Then the heterogeneous DEM model and DFN were integrated, and mechanical properties of CTB and failure mechanism were investigated on meso-level. The influence of material random field and microscopic initial defects on cracking behavior was further studied. The simulation results showed that the failure of CTB was mostly due to the accumulation of damage at mesoscopic level. Material heterogeneity results in stress concentration and induces microcracks. Initial defect was negative to structural strength but would increase the allowable failure deformation. The random particle model combined with microscopic initial defects could better characterize the mesoscopic cracking process of CTB materials. The present research provided a new numerical method for investigating the progressive failure process and the failure mechanism of cement-treated composites.

Using damage evaluation to assess the fatigue behaviour of cement-treated base material from laboratory and full-scale performance tests

Cement-treated base (CTB) has become the most popular cement-modified road-base material. This study theoretically connects understandings of CTB damage behaviour derived from laboratory and full-scale experiments using the continuum damage mechanics approach. Fatigue-life tests using four-point bending testing were performed on laboratory CTB specimens and compared to test data from full-scale fatigue testing conducted by the Australia Road Research Board. Damage evolution curves developed from both test environments were characterised and compared, resulting in three key findings: (1) damage evaluation through the normalisation technique can be reasonably used to overcome the inherently different conditions of the testing environment; (2) a significant distinction was observed in the final phase of the damage evolution curves; (3) damage evolution of field CTB can be reasonably predicted by the damage evolution of laboratory CTB specimens. Future research should investigate the effects of parent material gradation, testing method, and unforeseen factors to the damage characteristics of CTB.

Micro-scale characterization of the heterogeneous properties of in-service cement-treated base material

Compared with ordinary cement concrete, cement-treated base (CTB) material consumes much less cement and water, and its mechanical properties are also significantly different. The macroscopic properties of CTB are determined by microstructure. In order to understand the mechanical performance of in-service CTB, it is of great importance to investigate its microscopic structure and properties. In the study, the microscopic mechanical, structural, and chemical characteristics of the mortar and interfacial transition zone (ITZ) of in-service CTB were investigated through micro-scale characterizations. The results indicated the aggregate-mortar interface of in-service CTB is much weaker than that of concrete. A large number of micro-cracks and micro-pores were distributed in the ITZs and mortar. The micro-scale modulus of ITZ was approximately 85.6% of the modulus of the mortar and showed high variance. More compacted cement paste structure is beneficial to improve the mechanical properties of CTB.

New Procedure for Compacting Prismatic Specimens of Cement-Treated Base Materials

Understanding the long-term behaviour of cement-treated base materials is a key factor to improve its design and obtain environmentally friendly pavement base materials. Their characterization requires manufacturing prismatic specimens. However, various authors highlight the absence of standardized test methods for fabricating beams in the field and laboratory, which is not an easy task because it depends on the qualification and experience of the testing team. The aim of this paper is to present a new device and procedure for compacting prismatic specimens of cement-treated base materials. In this research, it was used for compacting soil-cement to simulate its performance as a road base material. This device employs elements that are generally available in a concrete laboratory test, such as a vibrating table or prismatic moulds. Once the procedure was established, and in order to verify its suitability, flexural and compressive strength tests were carried out. Results showed that the values obtained were consistent with this material and, despite the heterogeneity of the material, specimens from the same batch provided similar results and, hence, validated the compaction process. This new compacting procedure can improve understanding of the long-term performance of cement-treated materials from flexural and fatigue tests.

The Performance of Controlled Low-strength Material Base Supporting a High-volume Asphalt Pavement

A lack of proper base and subbase materials in pavement construction is one of the common problems in the tropical region worldwide. In many countries such as Thailand, cementitious materials are usually used for ground improvement. Controlled Lowstrength Material (CLSM) was considered in this study as a pavement base material. The CLSM mixes were prepared by varying cement, fly ash and fine aggregate content. Each mixed component was studied for their physical and chemical properties. After mixing, properties of the CLSM were investigated based on the standard testing of fresh concrete and cement-treated base material. The flowability, setting time and bleeding were checked to ensure that the CLSM were self-compacting. The mechanical properties of hardened CLSM were determined by means of CBR, unconfined compressive strength and resilient modulus tests. The resilient modulus results were used in the analytical design of flexible pavement with CLSM base. The critical traffic data under high-volume road collected by the Thailand Department of Highway was adopted in this study. Results show that the CLSM base considerably increased the performance as well as design life of asphalt pavement compared with the conventional crush rock base pavement.

Damage Behavior of Cement-Treated Base Material

Cement treated base (CTB) is a cement stabilized material which becomes more important to a modern road pavement under a better performance perspective. However, CTB has the inherent characteristic of fatigue deterioration corresponding to damage evaluations under repeated loading; but relatively rare fatigue and damage studies of CTB have been performed. Therefore, damage developments of CTB specimens tested under different loading conditions were characterized in this study. This because stress/strain state and fatigue life of materials are all related to their damage evolutions. Results from unconfined compressive tests revealed that damage evolutions of CTB specimens depended on the monotonic-compressive loading rates. Moreover, the cyclic flexural beam tests were also performed to determine the fatigue damage evolutions of CTB specimens. The test results showed that damage evolutions of CTB specimens subjected to cyclic bending forces were influenced by the levels of applied strain. However, the damage evolutions were independent from the loading waveforms. In addition, the prediction models for damage evolutions of CTB were also developed in this study. The natural logarithmic model was found to provide the most reliable values of predicted damage variable compared to the other mathematical models used in this study. It was also discovered that regression parameters of the developed model can be estimated by the function of an applied strain level. Furthermore, this study reveals that the fatigue behavior of CTB specimens can be predicted based on the damage variables.

Dynamic Modulus Measurements of Bound Cement-Treated Base Materials

AbstractOne of the most common methods used in road-pavement construction is the stabilizing of the conventional pavement base course layer. This is achieved by adding cement or lime to gain better material performance. However, obtaining modulus input parameters from a cement-stabilized base course layer for pavement-response analysis under real traffic conditions has proven difficult in that, to date, only ambiguous results have been produced. Using the flexural modulus or elastic modulus in the response analysis has certain limitations in embracing real pavement behavior under traffic and temperature conditions. Accordingly, a more reliable modulus input parameter for pavement analysis under traffic (cyclic) loads is required to obtain more precise and reliable outputs. Moreover, there is, at present, no test protocol to determine a suitable modulus for a cement-stabilized base material under the cyclic loading regime. This study aims to examine the real dynamic responses of cement-stabilized base course materials with a view to adapting the asphalt mixture performance tester (AMPT), a specifically designed dynamic modulus test machine used on asphalt concrete material. The AMPT dynamic modulus test has as an advantage in that loading and temperature regimes based on real pavement conditions can be rationally simulated and directly applied to the test samples. As such, the dynamic moduli of a cement-stabilized base course material can be obtained under different temperature and loading rates. Moreover, the effects of the dynamic strain range, cement content, and curing duration on the dynamic responses of a cement-stabilized base course material may also be examined. Cement-stabilized base course materials of 4 %, 5 %, and 6 % cement contents (by mass) were used as the study materials. The findings of this study indicate that curing durations and cement contents significantly influence the dynamic modulus values of cement-stabilized base course materials. However, the dynamic modulus is insignificantly affected by the changes in temperature and loading rates within a specific range of testing conditions in this study. The test results also reveal that cement-stabilized base course materials under examination behave in the manner of an elastic material when subjected to an axial compressive deformation of 45–105 μstrains. This is because of the dynamic modulus having no impact upon changes in the dynamic strain ranges or on the magnitudes of cyclic loads. Moreover, the dynamic moduli from this study were found to be much higher than the elastic moduli suggested by previous studies. However, the flexural moduli, which are derived from standard flexural tests, demonstrated close values to those of the dynamic moduli obtained in this study. In the study, the dynamic modulus of cement-stabilized base course materials, derived from the dynamic modulus using AMPT, could more reasonably embrace the dynamic responses of a material under traffic-loading conditions. This leads to a somewhat more reliable modulus input for the cement-stabilized base course materials used in a rational pavement design and analysis method.

Impact of the implementation of continuous construction method on pavement cracking performance

A continuous construction method (CCM) was proposed to decrease the reflective cracking generated from the cement-treated macadam base by reducing the shrinkage of base materials and improving the bond strength at the interface between the base layer and surface layer. Traditional 3–7 days of curing period of cement-treated macadam base was eliminated by CCM and the asphalt mixture can be paved immediately after the construction of cement-treated macadam base. An anti-cracking agent was developed and added into the cement-treated base materials to prolong the hydration process and improve the shrinkage performance of base materials. The influences of anti-cracking agent on the properties of cement-treated materials were analysed using laboratory tests. The generation of micro-expansion ettringite from cement system was investigated from the microscopic perspective using the scanning electronic microscope test. Test roads were constructed and contrasted to demonstrate the feasibility of this approach and showed a superior anti-cracking performance.