Crack Behaviour Under Vehicular Loading Along Mbagathi Road in Nairobi County
Abstract
Nairobi County has nearly 100% road network as bituminous roads and only 4km road
network (Mbagathi Road) is concrete road. This road was a pilot project that was
implemented by Kenyan Government between the years 2005 and 2007 at a total construction
cost of over 400 million Kenya Shillings. The design was done based on South Africa design
procedure on a 210 mm thick Plain Jointed Concrete Pavement (PJCP). Performance of Plain
Jointed Concrete Pavement (PJCP) depends on aggregate interlock, which is the mechanism
by which loads are transferred from one slab to the adjacent one. This study attempted to use
the information on load transfer mechanics in order to quantify the effect of aggregate
properties to crack size as well as the propagation of any cracks formed in service. Modern
methods applied during the design of concrete pavement do not consider fracture mechanics
into consideration. These make scheduling of repair and other maintenance works difficult.
This research was undertaken in two different ways namely experimental and computer
simulation. The experimental approach entailed measuring widths and depths of cracks
existing in Mbagathi road, and also involved setting up concrete beams in the laboratory and
loading them to failure with predetermined loads and measuring sizes of resulting cracks. On
the other hand, the computational approach was verified by experimental results entailed
simulating crack widths and depths with recent devised fracture models.
Cracks were experimentally noticed to occur due to loading the pavement with vehicular
loads bigger than safe load determined as 430.4kN. Cracks generated had crack width
equivalent to the measured flexural deflection and for an ideal concrete pavement crack width
and crack depth exhibited an exponential relationship. Experimental set-up yielded a
deflection load curve that showed a quintic relationship, the maximum deflection recorded
was 0.35mm.
It was found that vehicular loads induce stresses in concrete pavements which exceed
permissible tensile stresses, hence a better understanding of the resultant cracks, as well as
their propagation. Aggregate properties found to have an effect to crack width and depth were
water to cement ratio, hardness and surface texture. This research will lead to an
improvement of the design of concrete pavements in Kenyan environment.
Publisher
University of Nairobi
Rights
Attribution-NonCommercial-NoDerivs 3.0 United StatesUsage Rights
http://creativecommons.org/licenses/by-nc-nd/3.0/us/Collections
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