W. K. Mampearachchi

Finite-Element Model Approach to Determine Support Conditions and Effective Layout for Concrete Block Paving

Concrete block paving (CBP) is one of the predominant road construction methods used in most of the developing counties due to its economic adaptability. It has emerged as a cost-effective road construction method suitable for different ground conditions but this has yet to be developed as a full fledged technique because of the dearth of technical expertise and knowledge. The aim of this research is to evaluate the state of support conditions and to discover effective patterns which can be used to improve concrete block paving technology. Development of a laboratory scale CBP model and evaluation of support conditions were mainly considered in the initial stage of this study. A developed laboratory scale CBP model was used to measure deflection basin with four different load arrangements. A three-dimensional finite-element model was built to measure elastic deflection behavior of concrete block pavement with SAP2000 structural analysis software. This finite-element model was used to simulate field conditions of a concrete block pavement and it was verified with the deflection values observed in a laboratory scale model. The verified analytical model has been used to perform a parametric study in order to determine necessary improvements for weaker support conditions and find effective laying arrangement in the concrete block paving. Developed design charts and field observations can be used to propose subgrade improvement methods for weaker support conditions. The writers recommend concrete block laying work for low volume roads with subgrade strength higher than 10% CBR. The results indicate that herringbone bond pattern performed well under effect of vertical loading and breaking action. It has the capability to develop better interlocking action in CBP work.

Analytical Model for Passing Sight Distance Design Criteria of Two-Lane Roads in Sri Lanka

Abstract For a safe overtaking manoeuvre on two-lane highways, drivers need a sufficient sight distance along the roadway, but it depends on the traffic environment. To provide an adequate Passing Sight Distance (PSD), a number of models have been proposed since the initial model introduced by American Association of State Highways and Transport Officials (AASHTO) in 1954. It is a current design practice in Sri Lanka as well, however, not validated for local traffic conditions. This paper will present an alternative PSD model and an evaluation of AASHTO model for national highway design. Experiment was based on GPS data collection. In conclusion, PSD demand was satisfied by AASHTO PSD under mix traffic conditions, but not the safety concerns for speeds greater than 80 km/h, while alternative model successful for all speeds.

Finite element modelling approach to determine optimum dimensions for interlocking concrete blocks used for road paving

Interlocking concrete block paving (ICBP) is one of the foremost construction methods used in most of the developing countries due to its economic benefits. Although it has emerged as a cost-effective paving material, it is yet being developing as a full-fledged construction technique. The aim of this study was to develop a finite element modelling (FEM) approach to determine optimum dimensions for concrete blocks and to evaluate the deflections and stresses induced in pavements with the application of loads. A three-dimensional FEM was built using the ANSYS FEM software to analyse pavements with different block shapes and laying patterns. Uni 3 block in a herringbone bond pattern induced the lowest deflections and stresses, and therefore the dimensions of Uni 3 block were considered as the optimum dimensions in this analysis. Based on that, a new block shape which incorporated the same behaviour was proposed. Angles 110° and 100° were recommended instead of 137° for the uni-style block shape. Furthermore, the stress and deflection distributions observed in the pavement for a change in the wheel wander indicated significant variations in the stresses when the wheel wander was closer to the pavement edge.

Validity of aggregate packing models in mixture design of interlocking concrete block pavers (ICBP)

Interlocking concrete block pavers (ICBP) are manufactured using a semi dry concrete mix and vibration and compression are applied by electrical or hydraulic machines to cast the blocks. Hence the concrete mixture characteristics differ from concrete mixtures that we use for general purposes. When determining the mix proportions for the mix design, several properties of the block need to be considered. Maintaining required strength and surface texture, producing mixes with optimum water content to maintain the green strength while avoiding slumping are some of the challenges faced by the industry. To overcome such challenges a mix design using aggregate packing optimisation can be used effectively. There are number of theoretical packing models available for concrete mix optimisations and each model has its own pros and cons. Most of the models are successfully used for more generalised concrete applications and these models have not been used for more specialised applications such as ICBP. This study considers Modified Toufar model, three parameter model and compressible packing model to determine the validity of applying for ICBP. The theoretical models are compared with laboratory and field packing density experiments and the results indicate that the models are not accurately predicting the packing density for mix design of ICBP. Hence the study suggests developing a new theoretical packing model that accommodates production procedures together with mixture performances to enhance the mix design procedure as well as the performance of ICBP.

New block design and laying parameters for interlocking concrete block pavements to improve human thermal comfort levels in urban spaces

AbstractAsphalt, concrete and interlocking concrete block paving (ICBP) are the most commonly used paving materials. Artificial pavements are one of the key factors for the urban heat island effect. Due to high irradiance, the ambient air temperature rises above human thermal comfort levels. Studies have shown that ambient air temperatures above asphalt and concrete surfaces are significantly higher than those above ICBP pavements. Typically, paving blocks are used in public spaces that are generally used by pedestrians. During the daytime, the surface temperature of pavements rises and walking on pavements becomes very uncomfortable. The thermal behaviour of interlocking concrete block pavements is mainly governed by solar irradiation. When pavements are exposed to solar radiation, paving blocks are heated and the temperature of their top surfaces rises. Several factors such as heat capacity, convection film coefficient, and heat conductivity directly affect the temperature of ICBP. In this study, a fini...

Development of a polymer-modified bitumen specification based on empirical tests – case study for Sri Lanka

Pavements with polymer modification exhibit greater resistance to permanent deformation, less thermal cracking, less fatigue damage and less temperature susceptibility. Implementation of polymer-modified bitumen (PMB) is currently taking place in developing countries and the absence of PMB specification has always been a constraint. This research was aimed at developing a testing procedure for PMB, based on test methods that are currently available in Sri Lankan laboratories. The test methods were selected considering the adequate control of binder properties during application and usage. Penetration test is included to control the intermediate temperature properties and identify binder grades. Softening point test controls the high-temperature properties while viscosity test controls the mixing and compaction temperatures. Elastic recovery test and solubility test were employed in order to identify the presence of polymer in PMB. Storage stability test determines the separation tendency of polymer from bitumen. Flash point limits are set for the application safety. Thus all the essential parameters of bitumen are controlled by the proposed specification. The acceptance limits are determined considering different PMB specifications of several other countries, past research outcomes and laboratory test results. The proposed specification which is based on empirical test methods facilitates adequate quality control of PMB and it would be a useful guideline for the implementation of PMB for hot mix asphalt in Sri Lanka.