Performance, evaluation, and enhancement of hydrated cement treated crushed rock base (HCTCRB) as a road base material for Western Australian roads

Hydrated Cement Treated Crushed Rock Base (HCTCRB) is produced by mixing a standard crushed rock base with 2% cement (by mass) and water then a re-mixing process is performed after the specific hydration period. This technique improves the engineering characteristics of the materials while still maintain the unbound properties. Performance evaluation of HCTCRB was investigated with variation of factors during manufacturing and construction. Finally, the experimental results were implemented for the pavement analysis and design

Permanent Deformation Behavior of a Cement-Modified Base Course Material

AbstractOne of the major failure modes in flexible pavements having thin asphalt surface associates with rutting or permanent deformation in a base course layer. Thus the material characterisation in term of permanent deformation is important for the mechanistic-empirical pavement design. This study investigated the permanent deformation behaviour of a modified granular material used for the base course layer. According to the Austroads definition, modified granular materials are granular materials stabilised by adding a small amount of stabilising binder such as bitumen, cement or pozzolanic material. The performance of the original materials is thus improved with regard to aspects such as strength, plasticity, and moisture susceptibility. However, the improvement of tensile strength is not one of the purposes of stabilisation. Hydrated cement treated crushed rock base (HCTCRB), which is stabilised with cement, was used for this study. HCTCRB is made by blending standard crushed rock base (CRB) with 2% cement (by mass of dry CRB) at the optimum amount of water. Then the fresh mixture is cured for specified hydration periods. Consequently, the hydrated mixture is returned to the mixer to break the cementitious bonds generating during the hydration reaction. This procedure aims to produce a cement-modified material whilst maintaining unbound base course characteristics. This study evaluated the effect of hydration period and moisture content on the permanent deformation of the material. The hydration periods of the test specimens varied from 7 to 28 days. The moisture contents ranged from 60% to 100% of OMC, by wetting and drying the specimen. It was found that the moisture content of samples significantly influenced the performance of HCTCRB. However, a consistent performance trend over various hydration periods was not conclusive

Performance of Hydrated Cement Treated Crushed Rock Base as a Road Base Material in Western Australia

Hydrated Cement Treated Crushed Rock Base (HCTCRB) is produced by adding 2%-Portland cement with standard crushed rock base. The mixture is disturbed after the specific hydration period to prevent setting up and retain its unbound property. HCTCRB has been commonly adopted for Western Australian roads, however based on empirical method and experiences. Thus, the characterisation of HCTCRB following the pavement mechanistic approach is needed. This paper aims to presents the performances of HCTCRB in terms of permanent deformation and resilient modulus. The repeated load triaxial tests were performed to study the performances of HCTCRB that affected by manufacturing (hydration period) and construction procedures (amount of water added during compaction and dry back). This study has found that HCTCRB exhibited the stress dependent behaviour. All these studied factors significantly affect the resilient performances of HCTCRB in dissimilar trends. The certain impact on the material performances related to the hydration periods still could not be concluded. The higher water addition even at the optimum moisture content of HCTCRB resulted in the poorer performances, although it induced the higher dry density, which indicated that the HCTCRB is still susceptibility to moisture content. The dryback process has potential to improve the material performances of the material in different level which depends on amount of additional water. All the tested results indicated the significant influence of moisture content to the performances of HCTCRB with regardless of the dry density

Characteristics and Performance of Cement Modified–Base Course Material in Western Australia

Hydrated Cement Treated Crushed Rock Base (HCTCRB) is produced by adding 2% Portland cement (by mass) to a standard crushed rock base (CRB) at an optimum moisture condition. The unique production process for HCTCRB is different from that of a common cement-treated base in that a re-mixing process is performed after the hydration of cement, preventing cementitious bonding to maintain the unbound material characteristics with an improvement in material engineering properties. This paper presents the resilient modulus (MR) and permanent deformation (PD) characteristics of HCTCRB after variable hydration periods, water addition during compaction and dryback. The difference in material hydration periods affected the performance of HCTCRB. However, in this study, a consistent performance trend with various hydration periods could not be found. Moisture contents have major influence on the properties of HCTCRB. The results indicate that a higher moisture content gives a more increase in PD and a more decrease in MR of this material. Addition of more water during compaction caused inferior PD and MR performance even though the samples achieved a higher dry density. A dryback process to achieve a dryer condition can improve material performance. After samples were subjected to a dryback process, it was found that samples prepared by adding water during compaction showed a decrease in material performance comparing to samples that were compacted without additional water. Thus, the amount of water addition to mixes during compaction must be controlled

Characterisation, Analysis and Design of Hydrated Cement Treated Crushed Rock Base as a Road Base Material in Western Australia

Hydrated Cement Treated Crushed Rock Base (HCTCRB) is widely used as a base course in Western Australian pavements. HCTCRB has been designed and used as a basis for empirical approaches and in empirical practices. These methods are not all-encompassing enough to adequately explain the behaviour of HCTCRB in the field. Recent developments in mechanistic approaches have proven more reliable in the design and analysis of pavement, making it possible to more effectively document the characteristics of HCTCRB. The aim of this study was to carry out laboratory testing to assess the mechanical characteristics of HCTCRB. Conventional triaxial tests and repeated load triaxial tests (RLT tests) were performed. Factors affecting the performance of HCTCRB, namely hydration periods and the amount of added water were also investigated. It was found that the shear strength parameters of HCTCRB were 177 kPa for cohesion (c) and 42° for the internal friction angle (f). The hydration period, and the water added in this investigation affected the performance of HCTCRB. However, the related trends associated with such factors could not be assessed. All HCTCRB samples showed stress-dependency behaviour. Based on the stress stages of this experiment, the resilient modulus values of HCTCRB ranged from 300 MPa to 1100 MPa. CIRCLY, a computer program based on the multi-layer elastic theory was used in the mechanistic approach to pavement design and analysis, to determine the performance of a typical pavement model using HCTCRB as a base course layer. The mechanistic pavement design parameters for HCTCRB as a base course material were then introduced. The analysis suggests that the suitable depth for HCTCRB as a base layer for WA roads is at least 185 mm for the design equivalent standard axle (ESA) of 10 million

Recycled Concrete Aggregates in Roadways: A Laboratory Examination of Self-Cementing Characteristics

This paper examines the self-cementing phenomenon of the road construction material known as recycled concrete aggregate (RCA). Two RCA types were selected as study materials: (1) high-grade RCA (HRCA), a quality RCA manufactured from relatively high-strength concrete structures; and (2) road base RCA (RBRCA), a high-grade RCA blend combined with brick and general clean rubble (road base material). Laboratory tests were performed to obtain the unconfined compressive strength, indirect tension dynamic modulus, and resilient modulus of the test samples to examine their hardening characteristics when subjected to varying curing periods. These tests were performed in conjunction with microstructure analyses from X-ray diffractometry (XRD) and scanning electron microscope (SEM) techniques. The HRCA samples, which were prepared and subjected to varying curing conditions, transformed from an initially unbound material into a bound (fully stabilized) material. The results of XRD and SEM analyses clearly demonstrate that secondary hydration occurred. The RBRCA samples were able to maintain their unbound granular properties, with nonsignificant self-cementing, thus supporting the hypothesis that the mixing of nonactive materials such as bricks and clean rubble into RCA will lessen the tendency of RCA toward self-cementing

Pavement Analysis and Design for Hydrated Cement Treated Crushed Rock Base (HCTCRB) Pavements

Hydrated Cement Treated Crushed Rock Base (HCTCRB) is a cement modified basecourse material which the mixture of a standard crushed rock base and cement is disturbed after hydration. The unique production process for HCTCRB is different from that of a common cement-treated base to prevent cementitious bonding in order to maintain the unbound material characteristics with an improvement in material engineering properties. This paper presents the mechanistic-empirical pavement analysis and design for flexible pavements containing HCTCRB basecourse. The resilient modulus presenting the stress dependency behaviour of HCTCRB derived from the repeated load triaxial tests were used as one of the input for the analysis and design. Pavement analyses in this study covered various states of materials i.e., linearity or non-linearity, and isotropy or anisotropy of pavement materials. A three - dimensional finite element analysis of pavement structure was also carried out. The conventional pavement analysis in Australia by Circly software, using the anisotropic and quasi-non-linearity technique, is still deemed reliable in comparison with the various approaches examined in this study. However, there remains a concern regarding the reliability of the single input value of the resilient modulus derived from the resilient modulus tests. The average resilient modulus from the test results appeared to be too high for an effective analysis to be undertaken. Based on the stress-dependent analyses conducted and concerned with the thickness range of the basecourse layer, a typical value for the resilient modulus of HCTCRB was determined

Mechanical behaviours of a base course material in Western Australia

Hydrated Cement Treated Crushed Rock Base (HCTCRB) is produced by adding 2% Portland cement (by mass) to a standard crushed rock at an optimum moisture condition. The unique production process of HCTCRB different from that of a common cement treated base is the remixing process which is performed after the hydration of cement. This prevents cementitious bonding and maintains unbound material characteristics with an improvement in material engineering properties. This study aims to examine the resilient modulus (MR) and permanent deformation (PD) of HCTCRB under various conditions of water addition during compaction and dryback. The results indicate that the higher the moisture content of HCTCRB, the poorer the PD and MR performance. Higher addition of water during compaction causes the inferior PD and MR performance even though the samples achieved the higher dry density. The dryback process to achieve the dryer condition can improve the material performance. After the test specimens were subjected to the dryback process, it was found that the samples prepared by adding water during compaction resulted in poorer material performance in comparison to that of the samples that were compacted without additional water. Thus, the amounts of water added to mixes during compaction must be closely monitored

Engineering characteristics of cement modified base course material for Western Australian pavements

In North America, cement-modified soil (CMS) is described as a soil that has been treated with a relatively small amount of cement in order to improve its engineering properties and make it suitable for construction purposes. CMS leads to a typical soil stabilisation technique employed in Western Australian base course material: hydrated cement treated crushed rock base (HCTCRB), which incorporates an additional hydration process which differs from the original CMS technique. However, because the HCTCRB technique was developed mainly by an empirical approach based on pavement trials, it is posited that HCTCRB itself may be inconsistent with regard to fundamentals such as quality control and uniformity of elements. This then causes uncertainty during the application of HCTCRB with regard to its essential qualities, mix proportion, mixing and curing processes, and construction processes. The effects of these ambiguities need to be better understood in order to maximise the application of this material to new pavement design methods where reliability and consistency is crucial.This study aimed to comprehensively investigate the effects on HCTRB of the amounts of mixing water added, hydration period, and compaction effort on physical properties (ie. gradation and surface properties), and mechanical properties (ie. shear strength parameters, resilient modulus and permanent deformation) using scanning electron microscopy (SEM), conventional triaxial tests and repeated load triaxial tests. HCTCRB demonstrates superior performance to the original material in terms of resilient modulus and permanent deformation. SEM and static triaxial tests revealed that crushed rock base shows higher internal friction angles but less cohesion than HCTCRB. The hydration period of HCTCRB during the manufacturing process was found to have an insignificant effect on particle size distribution. However, hydration period does affect the permanent deformation and resilient modulus characteristics of HCTCRB

Characteristics of Hydrated Cement Treated Crushed Rock Base (HCTCRB) for Western Australian Roads

Hydrated Cement Treated Crushed Rock Base (HCTCRB) is a unique base course material instigated and broadened in Western Australia roads. The HCTCRB concept was originated by blending small amount (1 to 2% by mass) of Portland cement with standard crushed rock base (CRB) at an optimum amount of water. The mix is stored for some specific hydration periods (7 to 90 days) and then remixed in order to break the cementitous bond before construction. HCTCRB was initiated, and being developed, to accomplish the disadvantages of conventional CRB and cemented treated crushed rock base which tends to exhibit the fatigue deterioration. HCTCRB is expected to provide higher shear strength and lower moisture sensitivity than CRB while avoid significant tensile strength and bound characteristic that lead to fatigue and crack problems as appear in cement treated base. Nevertheless, its application is in doubt regarding the proper qualities and proportion of mixing materials, mixing and curing process, and construction procedures. Thus, effects of such abundant factors governing the HCTCRB properties during manufacturing and construction have to be more investigated. This research exhibits the physical and performance characteristics of HCTCRB -in comparison with that of standard CRB. The experiments were conducted in various conditions (hydration periods, moisture contents, and degree of compaction) to examine the physical properties such as gradation and surface property, and performance characteristics such as shear strength parameters, resilient modulus and permanent deformation. The research outcome leads to further enhancement of HCTCRB using mechanistic approach for analysis, design and modelling