Precision Estimates and Statements for Performance Indices from the Indirect Tensile Cracking Test at Intermediate Temperature

The Virginia Department of Transportation (DOT) has taken initiatives to implement the Balanced Mix Design (BMD) method to assure the long-term service life of its pavement network from a mixture quality standpoint. As part of this initiative, the cracking tolerance (CT) index obtained from the indirect tensile (IDT) test at intermediate temperature in accordance with ASTM D8225-19 was selected for evaluating the cracking potential of dense-graded surface asphalt mixtures. This prompted the need to generate the precision estimates (repeatability and reproducibility) for the test method for proper implementation during quality measurement practices. Thus, this interlaboratory study was undertaken to determine the precision estimates of the CT index calculated from the IDT test and to develop the associated precision statements. In addition, fracture strain tolerance (FST) and indirect tensile strength were included. Two asphalt mixes with significantly different CT index values were designed for the evaluation. Forty-six pairs of five replicate sets of compacted specimens (one set for each mix) were sent to 41 participating laboratories to be tested at 25°C. The test results were checked for data quality. The effects of loading rate and manufacturers on the indices were also evaluated. The test results indicated that one third of the sets were not tested in full accordance with the ASTM standard, indicating a need for training. The results also indicated that the specified loading rate of 50 ± 2 mm/min in ASTM D8225-19 for the IDT test may need revision. Finally, the precision estimates and associated statements for the three indices were presented.

Characterization of Clay Soil and Zolite Powder as Materials for the Production of Irrigation Porous Pipes

The uses of clay pipes in irrigation water management are becoming popular, especially in arid and semi-arid soils. The study examined clay and zeolite materials for irrigation pipes, and this paper reported characteristic properties of these materials. Hydrometer, pychnometer and core sampler methods were for soil physical properties determination. Consistency tests using (Atterberg method) and analytical techniques (Scanning Electron Microscopy, SEM and Energy Dispersive Spectroscopy, EDS) for samples analyses. The results indicate the soil to contain 11 % sand, 34 % silt and 55 % clay fractions and texturally classified as clay with a particle density of 1.58 g/cm3 and bulk density 2.43 g/cm3 respectively. Addition of zeolite at 3:1 clay/zeolite mix ratio shows liquid limit (LL) and plastic (PL) values to decreases from 50.7% to 43.7% and 27.6% to 27.3% while plasticity index, (PI) change from 23.2 to 16.7 respectively. The shrinkage rate decreases from 11.67% for raw clay to 8.92 % for the treated sample. The EDS analysis shows both clay and zeolite samples to contain carbon, silica (SiO2) and alumina (Al2O3) as the major constituents with ferric oxide (Fe2O3), potassium oxide (K2O) and cobalt (Co) as the minor constituents. The major constituents contribute 89.26 and 94.4% while minor contribute 10.74 and 5.59 % in clay and zeolite samples. Modifying clay improved its workability, reduces cracking potential and absorption capacity and performance of porous clay pipes.

Restrained Stress Development in Hardening Mortar Internally Cured with Superabsorbent Polymers under Autogenous and Drying Conditions

This study reports the results of a series of experiments, particularly paying attention to the early-age behavior and response of hardening mortars incorporating different types and contents of superabsorbent polymer (SAP) under autogenous (sealed) and drying shrinkage (unsealed) conditions. To achieve this primary aim, the effects of SAP type (i.e., cross-linking density and grain size) and content on the internal relative humidity (IRH) changes and corresponding free shrinkage behavior, restrained stress development, and cracking potential of the mortar were extensively measured and analyzed, along with their strength and set time properties. The results of this study have shown that the internal curing (IC) via SAP effectively counteracted the early-age residual stress build-up due to autogenous shrinkage, as many other former studies described. No or little tensile residual stresses due to autogenous shrinkage took place when more than 0.4% SAP was added, regardless of the SAP type. However, it should be mentioned that the addition of SAP, irrespective of its content and type, hardly improved the shrinkage cracking resistance of the mortar when directly exposed to drying environment at early ages.

Middle-Up Cracking Potential in Flexible Pavements with Stabilized Foundations

This investigation presents a new perspective on the structural behavior of stabilized foundation pavements through full-scale testing and simulation where the historical premise of bottom-up fatigue cracking has been challenged. Two full-scale pavement sections were constructed at the National Center for Asphalt Technology Test Track in 2018. One section featured a stabilized foundation under the asphalt layers while the other was a thick-lift asphalt section on conventional base and subgrade materials. Both sections were embedded with pavement response instrumentation and their behavior was observed over time under accelerated truck trafficking. In addition, computational simulations were executed to explain the observed behavior. The strain measurement at the bottom of the asphalt concrete (AC) for the thick-lift section showed a familiar trend in which the tensile strain at the bottom of the AC increased exponentially with temperature. In contrast, the strain at the bottom of the AC in the stabilized foundation pavement was predominantly in compression at elevated temperatures. Further analysis revealed that compressive strain at the bottom of the AC increased exponentially with temperature similar to conventional flexible pavements but with a reversed sign. The results were confirmed by falling weight deflectometer testing that was conducted directly above the embedded pavement sensors. Computational simulations confirmed the behavior and suggested that the maximum tensile strain could occur at shallower depths, possibly mid-depth of the AC, in stabilized foundation pavements. This indicates stabilized foundation pavements could be prone to middle-up cracking and subsequent precautions should be taken to avoid middle-up fatigue cracking.

Numerical evaluation of horizontal cracking potential in continuously reinforced concrete pavement under varying saw-cut depths

<p>The objective of this study is to evaluate the horizontal cracking potential in terms of vertical tensile stress development near longitudinal steel bar in the continuously reinforced concrete pavement (CRCP). For this purpose, a three-dimensional (3D) finite element (FE) model of the CRCP segment with partial surface saw-cuts has been developed using the FE tool Diana 10.3. The early-age behaviour of CRCP subjected to external varying temperature field condition has been evaluated by using the staggered structural-flow analysis. The characteristics of the early-age crack pattern in terms of crack initiation and crack propagation obtained from the FE model are compared with the field observations of cracking developments on the CRCP sections in Belgium. The FE results indicate that the vertical tensile stress in concrete near the longitudinal steel bar develops at the transverse crack interface. It translates that the horizontal crack perpendicular to the vertical concrete stress can initiate from the transverse crack depending on the magnitude of stress against developing concrete tensile strength. It has also been observed that the deeper the saw-cut, the larger the magnitude of vertical tensile stress and the higher incident of horizontal cracking. Moreover, the developed 3D FE model can be further used to optimize the early-age behaviour of CRCP in advance of costly field trials.</p>