The performance of cemented pavement materials under heavy axle loading

Flexural beam fatigue strength evaluation of crushed brick as a supplementary material in cement stabilized recycled concrete aggregates

One of the major benefits of Accelerated Pavement Testing (APT) as a research tool is that the performance of pavement materials and structures can be evaluated at a reduced cost and in a short period of time. The Civil Infrastructure Systems Laboratory (CISL) for APT at Kansas State University was established in 1997. Six fatigue pavement sections that had 100 mm thick hot mix asphalt layer were constructed for APT in CISL. The sections had the same base and subgrade materials. The sections were instrumented using strain gauges and pressure cells to measure pavement responses under APT loading. They were loaded with a 100 kN single axle load at 20 °C. The main objective of this paper is to investigate the effects of binder content, binder grade, and mixture nominal maximum aggregate size (NMAS) on the mechanistic responses from the experimental sections. Stress, strains, deflections, and profile data were collected periodically. Normalized falling weight deflectometer (FWD) deflection data were used to back-calculate moduli using the EVERCALC software. Measured pavement temperatures were used to adjust back-calculated moduli to a temperature of 20 °C. The stiffer the binder, the lower the longitudinal strain, permanent deformation, and roughness, but the higher the transverse strain, stress on the top of subgrade in general, and back-calculated moduli. Higher binder content results in a higher longitudinal strain, transverse strain, stress on top of subgrade, permanent deformation, rut depth, and roughness. The larger the NMAS, the higher the transverse strain, back-calculated moduli, permanent deformation, and roughness, but the lower the longitudinal strain, stress on the top of subgrade, and rut depth.

A laboratory study was undertaken to evaluate the durability of lightly stabilized granular base material subjected to wet-dry (w-d) cycles using repeated load triaxial (RLT) test, unconfined compressive strength (UCS) test and flexural beam test. RLT and flexural tests were conducted on a typical granular base material stabilized with 1.5% cement-flyash (CF) binder and the test specimens were cured for 28 days. Two different CF binder contents of 1.5% and 3% were selected to stabilize the UCS test specimens which were then cured for 7 days. Cured specimens were then subjected to w-d cycles prior to the testing. RLT test studied the permanent and resilient deformation behaviour of lightly stabilized granular base material subjected to w-d cycles under cyclic loading whereas UCS and flexural beam test were carried out under monotonic loading to determine the UCS and Modulus of rupture (MoR). Irrespective of the testing, specimens stabilized with 1.5% binder deteriorated heavily and did not last for more than 4 w-d cycles. UCS specimens stabilized with 3% binder showed greater resistance to w-d cycles and remained integrated even after 12 w-d cycles. MoR was significantly affected by w-d cycles compared with other mechanical properties. This study indicates that evaluating the durability using permanent deformation from multi-stage RLT test or UCS test is a better approach than conducting resilient modulus test.

Expansive soil is widely distributed and often needs to be improved for engineering and construction needs. Using blast furnace slag and fly ash as precursors and NaOH as an alkali activator, a geopolymer was prepared to solidify expansive soil, and the effect of nano-SiO2 on the compressive strength and water stability of the geopolymer-solidified expansive soil was further studied. The effects of alkali addition ratio, nano-SiO2 addition ratio, and curing agent addition ratio on the unconfined compressive strength and water stability of the cured soil were studied through unconfined compressive strength tests, and the curing mechanism was analyzed by electron microscopy scanning. The experimental results showed that the unconfined compressive strength and water stability of geopolymer-stabilized soil first increased and then decreased with an increase in alkali activator dosage. The optimal dosage of alkali activator was found to be 12.5%. Furthermore, it was found that adding nano-SiO2 can further enhance the strength and water stability of solidified soil. When the content of nano-SiO2 was 3%, the unconfined compressive strength was increased by 15%. With an increase in the content of nano-SiO2 doped polymer (GFNS), the unconfined compressive strength and water stability of the solidified soil showed a trend of first increasing and then decreasing, reaching a peak at a content of 20%. The cementitious materials, such as hydrated calcium silicate and hydrated calcium silicate aluminate, generated by the reaction between nano-SiO2 and geopolymer played a role in bonding and filling in the solidified soil. Under the joint action of the two, the structural arrangement between the solidified soil particles became more compact, which improved the strength of the solidified soil.

In this paper, red mud and slag were used as the main cementitious materials, and desulfurization gypsum and exciter materials were mixed to prepare red mud-based cementitious materials with excellent performance. The mechanical properties of red mud-based cementitious material stabilized gravel material were investigated by carrying out the compaction test, unconfined compressive strength test, splitting strength test and fatigue performance test. The test results show that with the increase in the dose of cementitious material, the hydration is more significant, generating more hydrated calcium silicate (C-S-H) gel, which in turn makes the unconfined compressive strength and splitting strength increase to a certain extent. Adding exciter and desulfurization gypsum in the appropriate amount is conducive to improving the hydration of red mud, improving the structural compactness, and improving the mechanical properties, volumetric stability and seepage resistance of the cementitious material.

The effect of different ages and water-binder ratios on the mechanical properties of circulating fluidized bed combustion desulfurization slag cement-soil

Synthesis of cemented paste backfill by reutilizing multiple industrial waste residues and ultrafine tailings: Strength, microstructure, and GA-GPR prediction modeling

This paper presents an investigation on the properties of two types of cement kiln dust (CKD)-stabilized dredged sediments, silt and clay with a comparison to hydrated lime stabilization. Unconfined compressive strength (UCS) and California bearing ratio (CBR) tests were conducted to examine the optimal stabilizer content and classify the type of highway material. A strength development model of treated dredged sediments was performed. The influences of various stabilizer types and sediment types on UCS were interpreted with the aid of microstructural observations, including X-ray diffraction and scanning electron microscopy analysis. The results of the tests revealed that 6% of lime by dry weight can be suggested as optimal content for the improvement of clay and silt as selected materials. For CKD-stabilized sediment as soil cement subbase material, the use of 8% CKD was suggested as optimal content for clay, whereas 6% CKD was recommended for silt; the overall CBR value agreed with the UCS test. The reaction products calcium silicate hydrate and ettringite are the controlling mechanisms for the mechanical performance of CKD-stabilized sediments, whereas calcium aluminate hydrate is the control for lime-stabilized sediments. These results will contribute to the use of CKD as a sustainable and novel stabilizer for lime in highway material applications.

Impact of curing conditions on the mechanical properties and micro characteristics of alkali-activated material synthesized from industrial waste soda residue

Although ordinary Portland cement (OPC) is one of the most widely used construction materials in the world, its relatively weak tensile strength and fracture resistance limit wider structure applications. Carbon nanotubes (CNTs), having been identified as one of the strongest and stiffest materials on earth, are attractive candidates as nano-filaments in reinforcing OPC. The investigation of CNT reinforced OPC composites (CNT-OPC) is at a relatively early stage, and very limited research regarding the effectiveness of CNTs in enhancing the tensile strength or fracture toughness of OPC are available in open literature. The published results on testing of the CNT reinforcing effect often show large variations and sometimes contradict each other. Therefore, there is a significant need for further studies in this area to improve understanding of the reinforcing behaviour of CNTs in cement matrix, including dispersion of CNTs and the effect of CNT on OPC paste in terms of hydration, microstructure, tensile strength and fracture properties. This study builds on the earlier research on CNT reinforcement of the mechanical properties of OPC paste in Duan’s group in the Department of Civil Engineering at Monash University. Specifically, the objectives of this study are (1) development of high mechanical performance CNT reinforced OPC paste by considering the effect of dispersion and concentration of CNTs within OPC matrix, and (2) investigation of the reinforcing mechanisms of CNTs in cement matrix by estimating the post-peak softening behaviour of CNT-OPC paste and the interfacial bond strength between CNTs and cement matrix. In order to develop high performance CNT reinforced OPC paste, the dispersion and concentration of CNTs were studied. The combinations of chemical functionalisation (COOH functional groups on CNT surface), a polycarboxylate-based cement compatible superplasticiser (PC), and sufficient ultrasonication energy have been found essential to achieving homogeneous dispersion of CNTs in cement paste. An effective PC to CNT mass ratio of 8 is recommended to ensure effective dispersion of CNTs, at the same time maintaining satisfactory workability of CNT-OPC paste. Moreover, a CNT dosage-independent optimal ultrasonication energy for achieving mechanically superior CNT-OPC paste was found to be 50 J/ml per unit CNTs-to-suspensions weight ratio. The incorporation of CNTs (of 0.075 wt.% of cement) substantially enhanced the mechanical properties of plain cement. For example, Young’s modulus was improved by 31.5%, flexural strength by 49.9%, and fracture energy by 62.6%. Regarding the reinforcing mechanisms of CNTs within cement paste, the post-peak softening characteristics of CNT-OPC paste were investigated. It was found that the linear post-peak softening characteristics, including initial fracture energy and cohesive tensile strength of plain OPC paste (estimated using size effect tests with the assistance of cohesive crack-based finite element simulation), can be significantly improved by incorporating CNTs. Particularly, the enhancement of cohesive tensile strength may be attributed to the filling of CNTs in the nano-sized colloidal pores and bridging micro-sized capillary pores. On the other hand, the comparable brittleness numbers obtained for CNT-OPC and OPC pastes indicate the minor contribution of CNTs to the ductility of plain OPC paste. Based on cohesive tensile strength, the range of effective interfacial bond strength between CNTs and cement matrix was estimated to be from 9.5 to 24.5 MPa based on a micromechanics-based crack bridging stress-crack separation model for CNT reinforced composites developed in Duan’s group. This result suggests that the introduction of COOH functional group may enhance the interfacial bond property between CNTs and cement matrix, thereby resulting in improved mechanical performances. This project will provide key information to assist other researchers and practitioners to better understand and apply the novel CNT-cement composite with improved mechanical properties to the design of structures and codification.

In both the United States and the United Kingdom, slurry walls are used as vertical barriers to control groundwater flow and to contain contaminants as part of waste containment systems. In the United States, slurry walls are commonly constructed using soil-bentonite ~SB! and the barrier typically consists of a mixture of select soil, bentonite, and bentonite-water slurry. Alternatively, in the United Kingdom, the barrier wall comprises a mixture of cement, blast furnace slag, and bentonite-water slurry. After a comparison of the two techniques, this paper presents the results of permeability and unconfined compressive strength tests on twenty-one different mixtures of slag-cement-bentonite ~slag-CB!. The slurry wall materials tested in this study were prepared using sample formulations originating in the United Kingdom and materials originating in the United States. Unconfined compression tests were performed on samples after one month of curing, while permeability tests were performed after one, two, three, six, and twelve months of curing. For the mixtures tested and cured twelve months, two mixtures ~one having 20% cementitious material with 70% slag replacement and another having 15% cementitious material with 80% slag replacement! were found to have the lowest hydraulic conductivity s2 3 10 ˛8 cm/ sd. The data show that 0 to 60% slag replacement had little effect on hydraulic conductivity of the resulting slag-CB mixtures. However, the hydraulic conductivity drastically decreases as the slag replacement increases from 70 to 80%. As expected, the unconfined compressive strength increased as the cementitious material content increased from 10 to 15 to 20%. The slag-CB consolidates rapidly and has compression characteristics similar to other high moisture materials.

Nanotechnology Applied to Chemical Soil Stabilization

A synergistic method using ferrous sulfate and cementitious materials to solidify landfilled municipal sludge

The properties of soft clay can be seen from the compressive strength value through the unconfined compressive strength (UCS) test. Soft soil was less well used as the subgrade for construction. The aim is to determine the increase in the unconfined compressive strength and bearing capacity of the foundation due to the addition of lime and volcanic ash on soft soil. Soft soil has undrained shear strength < 25 kPa based on the unconfined compressive strength test. The unconfined compressive strength test has been conducted on the soil-lime mixture and soil-volcanic ash mixture of 3-12% respectively to the weight of dry soil. The highest unconfined compressive strength values were found in soils with 6% of lime and 9% of volcanic ash. The bearing capacity of the foundation on soil stabilized with 6% lime increased 13.7 times, while the bearing capacity of the foundation on the soil with the addition of 9% volcanic ash increased the ultimate bearing capacity of 8.7 times the bearing capacity of the foundation on soft soil. The bearing capacity of the foundation on lime stabilized soil is higher than the bearing capacity of the foundation on volcanic ash stabilized soil.

Unsuitable or poor quality subgrade material requires proper treatment in order to make the subgrade suitable for overlying top layers of pavement for road construction. Stabilisation of the subgrade layer using cement is a method to improve the strength and stiffness of the subgrade, minimising the risk of road damage such as permanent deformation and improve the long-term performance of the pavement. This paper details a study on the soil–cement stabilisation method for a low-volume road in Malaysia. The scope of this study involved mix design in the laboratory and site verification. The laboratory tests involved soil classification, compaction test, unconfined compressive strength and California Bearing Ratio (CBR) tests while site verification tests comprised of field density test and unconfined compressive strength tests. From the laboratory tests, it was determined that the type of soil for the study area (silty clay) was suitable to be stabilised using cement based on the results obtained from soil classification test and unconfined compressive strength achieved of more than 0.8 MPa obtained after the addition of 5% cement by weight. Field density test achieved more than 95% laboratory com paction density and unconfined compressive strength of 1.01 MPa, indicating that the method was successfully implemented as site. It is recommended that future research should be carried out on more sites and on different types of soil to determine the suitability of cement as additive for subgrade stabilization in Malaysia.