Three-dimensional (3D) tire-pavement contact stresses for two types of tires used by the truck industry (new generation wide-base tire [WBT] and dual-tire assembly [DTA]) were measured and compared. The testing matrix was composed of five loads () (26.6, 35.5, 44.4, 62.1, and 79.9 kN) and four tire inflation pressures () (552, 690, 758, and 862 kPa). The equipment used for measuring the 3D-contact stresses is described along with the testing procedure and the methodology followed during data processing. The effect of applied load and tire-inflation pressure on the variation of longitudinal, transverse, and vertical CONTACT STRESSES along the contact length of each tire type was analyzed. Differences in the distribution and magnitude of the aforementioned stresses were observed between WBT and DTA; these differences are an important factor linked to pavement damage caused by each tire configuration. This experimental effort is part of a national study to evaluate the effect of WBT on pavement damage and compare it to that of DTA.

This paper describes a nondestructive pavement testing system called the multidepth deflectometer (MDD), which is used to measure depth deflection profiles of pavements. Effective elastic moduli of multilayered pavement structures can be backcalculated from these measurements. This system was developed in South Africa during the late 1970s to enhance the extensive program of full-scale accelerated testing with the aid of the heavy vehicle simulator (HVS). The MDD consists of a series of up to six linear voltage differential transducers (LVDTs) installed vertically into the pavement at preselected depths in a relatively small-diameter hole. Normally the MDDs are anchored at a depth of approximately 2 m below the surface of the pavement. Resilient depth deflections are measured with the MDD in association with a moving load. Case studies of measured deflections and backcalculated effective elastic moduli are given for tests on an asphalt base, a granular base, a cemented base, and a concrete base pavement section. The results are interpreted and discussed in terms of the behavioral characteristics and pavement responses, including permanent deformations. It was found that: 1. Asphalt bases may become granular after extensive accelerated testing. 2. Crushed stone bases may become stronger as a result of trafficking. 3. Lightly cemented bases crush near the surface, thus weakening the layer. 4. One concrete pavement debonded from its subbase after 190 000 load repetitions.

Three-dimensional tire–pavement contact loads of two truck tires–-a new-generation wide-base tire (WBT) and a dual tire assembly (DTA)–-were measured and analyzed. Extreme and typical values of tire inflation pressure (552, 690, 758, and 862 kPa) and tire loading (26, 35, 44, 62, and 79 kN) were considered in the experimental program. The measurements were performed with the stress-in-motion Mk IV system at the Council for Scientific and Industrial Research in South Africa. Peak values in three directions were compared, and the importance of tangential contact stresses was highlighted. In addition, characteristic variations of the measurements in the longitudinal, transverse, and vertical directions were identified. A function depending on two regression parameters, applied load, and distance along the contact length was proposed to represent the contact load in the vertical and transverse directions. An analysis was performed on the measurements to obtain the regression parameters, and a simplified procedure was proposed to determine tire–pavement contact loads. The contact area and contact length of the WBTs and the DTA were also compared.

This paper describes pilot scale tests of a novel process for the neutralisation of acidic mine water. Leachate from a waste coal dump was neutralised with limestone, and iron, aluminium, and sulphate were removed. Specific aspects studied were: the process configuration; the rates of iron oxidation, limestone neutralisation, and gypsum crystallisation; the chemical composition of the effluents before and after treatment; the efficiency of limestone utilisation; and the sludge solids content. The acidity was decreased from 12,000 to 300 mg/L (as CaCO 3 ), sulphate from 15,000 to 2,600 mg/L, iron from 5,000 to 10 mg/L, aluminium from 100 to 5 mg/L, while the pH increased from 2.2 to 7.0. Reaction times of 2.0 and 4.5 h were required under continuous and batch operations respectively for the removal of 4 g/L Fe (II). The iron oxidation rate was found to be a function of the Fe (II), hydroxide, oxygen, and suspended solids (SS) concentrations. The optimum SS concentration for iron oxidation in a fluidised-bed reactor was 190 g/L. Up-flow velocity had no influence on the rate of iron oxidation in the range 5 to 45 m/h. Sludge with a high solids content of 55% (m/v) was produced. This is high compared to the typical 20% achieved with the high density sludge process using lime. It was determined that neutralisation costs could be reduced significantly with an integrated iron oxidation and limestone neutralisation process because limestone is less expensive than lime, and a high-solids-content sludge is produced. Full scale implementation followed this study.

In South Africa, an empirical characterisation of crumb rubber modified (CRM) bituminous binders has historically been the only means of predicting their performance in pavement layers, short of constructing pavement test sections. An improved characterisation is provided by means of rheological analysis using a dynamic shear rheometer (DSR). However, the heterogeneous morphology of CRM bitumen makes it a challenge to test using current methods and equipment. DSR testing of CRM bitumen requires a plate gap adjustment to avoid any influence by the rubber particles. This has been done by monitoring the effect of changing the DSR plate gap setting on the measured linear visco-elastic properties of the binder. An adjusted gap was adopted for rheological measurements so as to characterise CRM bitumen properties with ageing. But, the incomplete recovery of CRM binder from asphalt/seals makes it impossible to monitor the rheological properties of the in situ binder within a pavement layer. This has led to indirect methods of investigating relationships between tested properties of the pure CRM bitumen to those of the in situ binder.