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This study explores the bond strength of steel reinforcing bars in normal concrete (NC) and ultra-high-performance concrete (UHPC) with steel fibers, focusing on the behavior of lap-spliced rebars. Key variables such as rebar diameter (D), spacing (s), lap-splice length (L1), and hook length (L2) were evaluated to understand their impact on bond performance. Both NC and UHPC increase in bond strength with greater spacing and lap-splice length, with UHPC demonstrating significantly stronger bond characteristics due to its higher compressive strength. A novel predictive method for calculating bond strength is proposed, offering practical guidance for designing lap-spliced rebars in construction, and includes reduction factors tailored for realistic construction settings. This method achieves an error margin below ±16.5%, providing an accurate approach for practitioners. This rational method incorporates both engineering and economic considerations, particularly valuable for applications in precast concrete structures where enhanced bond performance and durability are essential.

Natural rubber (NR) is categorized as a natural elastomer having capacity to modify the properties of asphalt cement. Pre-vulcanized NR latex (PVL) and concentrated latex (CL) were selected as modifiers for asphalt binder penetration grade 60/70 in term of dry rubber content to asphalt binder (r/b) ratios by the total weight of the asphalt cement. The CL and PVL asphalt concrete (CL-AC and PVL-AC) samples were fabricated utilizing the Marshall method. Overall engineering properties of asphalt binder were improved by CL and PVL inclusion. The improved properties of asphalt binder had a direct impact on the enhancement of pavement performance, including Marshall stability, indirect tensile strength (ITS), indirect tensile resilient modulus (IT Mr), indirect tensile fatigue life (ITFL), and rutting resistance. The optimum performance (highest Marshall stability, ITS, IT Mr, ITFL, and the lowest rut depth) achieved at r/b = 3 % for both CL-AC and PVL-AC. For the same r/b ratio, the PVL-AC had better properties than CL-AC. For PVL-AC was found to have lower initial strain and higher ITFL than CL-AC under a specific cyclic load. Based on the developed distress model and mechanistic design approach, the calculated pavement thickness of CL-AC and PVL-AC was found to be insignificant under the same traffic volume, whereas the construction cost of PVL-AC was much more expensive. The CL-AC demonstrated superior cost-effectiveness compared to PVL-AC and conventional AC pavements for the same traffic volume.

ABSTRACT Fly ash and biomass ash have been widely accepted as waste materials substituting Portland cement. In this paper, the role of these two ashes on the strength development of [...]

ABSTRACT This paper analyzes the strength development in cement-stabilized silty clay based on microstructural considerations. A qualitative and quantitative study on the microstructure is carried out using a scanning electron [...]

This research studies on the usage of fly ash (FA) and rice husk ash (RHA) based geopolymers for improving the compressive strength of recycled concrete aggregate (RCA) to be a lightweight stabilised pavement base material. A mixture of FA from coal-burning power plants and RHA from rice milling process was used as a precursor while the liquid alkaline activator (L) was a mixture of sodium hydroxide solution (NaOH) and sodium silicate solution (Na2SiO3). Various RHA/FA ratios (between 100/0 and 0/100) and NaOH/Na2SiO3ratios (between 50/50 and 100/0) were used in this study. The FA-RHA-geopolymer stabilised RCA samples, at each NaOH/Na2SiO3ratio were prepared at the optimum liquid alkaline activator content (OLC) for unconfined compressive strength (UCS) tests. The UCS tests were conducted after 7, 28 and 60 days of curing. The test results indicate that the UCS of FA-RHA-geopolymer stabilised RCA increases as the RHA/FA and NaOH/Na2SiO3ratios decrease and the curing time increases. Based on the Department of Highways, Thailand, the 60/40 RHA/FA and 60/40 NaOH/Na2SiO3mix proportions are recommended for both low and high traffic volume roads with a low unit weight of 21.1 kN/m3. This research study confirms the potential of FA-RHA-geopolymer stabilised RCA as an alternative stabilised road base material.

Skid resistance value (SRV) is a significant parameter representing the road safety condition. The measurement of SRV at different times after the construction is time-consuming and costly. To accurately predict the reduction of SRV, the SRV reduction model has been developed based on the aggregate and asphalt concrete mixture characteristics and field cumulative traffic volumes. In this study, three main types of aggregates typically used in pavements in Thailand, being limestone, granite and basalt were used to make asphalt concrete. The standard dense-grade asphalt concrete mixtures of 9.5 and 12.5 mm maximum aggregate sizes were designed and constructed at the studied sites (12 project sites located in 6 provinces). The SRVs were measured at every 50,000 passenger car unit (pcu) by the British pendulum tester for 3–4 years after the end of construction. Based on the statistical analysis of the test results, the SRV at various cumulative traffic volumes can be predicted using asphalt concrete mixture characteristics and initial SRV (after the end of construction) as prime parameters. The model will be recommended for inclusion in the Department of Rural Roads, Thailand preventive scheme for road safety management protocols.

Pavement rehabilitation and reconstruction generate large quantities of reclaimed asphalt pavement (RAP). The improvement of the engineering properties of this RAP is required in order to enable it for use as environmentally friendly alternative construction material in road pavements. The durability of RAP when blended with crushed rock (CR) and stabilized with Portland cement was investigated in this paper. The CR replacement was found to improve the compactibility and durability of the stabilized RAP/CR material. For a particular RAP:CR ratio, the compaction curves of cement-stabilized RAP/CR blends were found to be essentially the same for all cement contents, but different for unstabilized blends; i.e., the maximum dry unit weight of cement-stabilized RAP/CR blends is higher than that of unstabilized RAP-CR blends. The wetting-drying (w-d) cycles led to a loss in weight of the cement-stabilized RCA/CR blends and to a subsequent reduction in strength. The w-d cycle strengths (qu(w-d)) for a state of compaction (dry side, wet side or optimum water content) at any w-d cycle could be approximated from the corresponding initial soaked strength (prior to w-d tests) (qu0). The qu0of cement-stabilized RAP/CR blends increased with an increasing CR replacement and an increasing cement content. Assuming that the CR replacement also results in an increasing cement content, w/[C(1 + kCRc)] was proposed as a critical parameter for developing qu0and qu(w-d)predictive equations where wis the water content at the optimum water content, Cis the cement content, kis the replacement efficiency, and CRcis the CR content. Based on the qu(w-d)predictive equation developed here, a design procedure for the laboratory mixing of cement-stabilized RAP/CR blends was proposed, which would be valuable for an accurate determination of the ingredients (RAP:CR ratio and cement content) required to attain the necessary strength at the design service life.

Laboratory oedometer tests were conducted to investigate the effect of small intermediate reloading–unloading (r-u) cycles (in over-consolidated range) on a general unloading path and that of small unloading–reloading (u-r) cycles on a general reloading path on the permanent deformation of Ariake clay samples. The test results indicate that the permanent deformation increased with r-u cycles, and decreased with u-r cycles. The test results were simulated well using an existing static u-r model. Then two case histories of land-subsidence were analyzed. The engineering significance of considering daily variations of ground-water levels on the simulated results has been confirmed by comparing with the field measurements.

This paper studies compaction characteristics and California Bearing Ratio, CBRvalues of fine-grained soils, lateritic soils and crushed rocks. All test data were collated from the Bureau of Rural Road 6, the Department of Rural Roads, Thailand. The Ohio's and the modified Ohio's curves can predict satisfactorily the compaction curves of the fine-grained soils, and lateritic soils and crushed rocks consistent with the grade B of the American Association of State Highway and Transportation Officials (AASHTO) requirement. The CBRvalue of a specific soil is directly related to the relative dry unit weight (the ratio of dry unit weight to maximum dry unit weight, γd/γd,max). The field compaction result of a fine-grained soil at the optimum water content, OWC, shows that initially the dry unit weight increases rapidly with the number of roller passes and the relationship between dry unit weight and number of roller passes is represented by the logarithm function. Finally, the dry unit weight reaches a constant value, which is close to the laboratory maximum dry unit weight. Even with a large number of roller passes (compaction energy), the dry unit weight cannot be enhanced further because the soil state approaches the zero air void state. In practice, the excess roller pass is thus not economic. Based on the analysis of the test data, the field compaction procedure for road embankment and pavement constructions, which includes the material selection and the construction control, is suggested. It is useful in terms of both engineering and economic viewpoints.

The in-situ deep mixing technique has been established as an effective means to effect columnar inclusions into soft Bangkok clay to enhance bearing capacity and reduce settlement. In this paper, an attempt is made to identify the critical factors governing the strength development in cement admixed Bangkok clay in both the laboratory and the field. It is found that clay-water/cement ratio, wc/Cis the prime parameter controlling the laboratory strength development when the liquidity index varies between 1 and 2. Based on this parameter and Abrams' law, the strength prediction equation for various curing times and combinations of clay water content and cement content is proposed and verified. This will help minimize the number of trials necessary to arrive at the quantity of cement to be admixed. Besides the wc/C, the strength of deep mixing column is controlled by the execution and curing conditions. For low strength improvement (laboratory 28-day strength less than 1,500 kPa), the field strength of the deep mixing columns, quf, made up from both dry and wet mixing methods is higher than 0.6 times the laboratory strength, qul. The quf/qulratios for the wet mixing columns are generally higher than those for the dry mixing columns. This higher strength ratio is due to the dissipation of the excess water in the column (consolidation) caused by the field stress. The water to cement ratio, W/C, of 1.0 is recommended for the wet mixing method of the soft Bangkok clay. A fast installation rate was shown to provide high quality for low strength columns. Suggestions are made for improving the deep mixing of soft Bangkok clay, which are very useful both from economic and engineering viewpoints.