Flexural Strength Assessment of Hollow Reinforced Concrete Filled with Polyvinyl Chloride (PVC) Pipe at Selected Positions

Abstract

Reinforced concrete (RC) beams are widely used in construction due to
their strength and durability, but the inclusion of openings is often
necessary to accommodate utilities such as pipes, ducts, and cables. This
study investigates the flexural strength of hollow reinforced concrete
beams with varying void placements. Six beam samples (500 mm × 100
mm × 100 mm) were cast using a 1:2:4 concrete mix and tested under
four curing periods: 7, 14, 21, and 28 days. Five beams were cast with
voids at different positions, and one served as a solid control. Supporting
material tests, including sieve analysis, water absorption, and slump test,
were also conducted to assess material suitability. The sieve analysis
revealed a well-graded sand (fine aggregate) with a uniformity
coefficient (Cu) of 7.00 and a curvature coefficient (Cc) of 1.02, making
it suitable for structural applications. Water absorption was found to be
4.6%, indicating moderate porosity and good durability, while the slump
value of 75 mm confirmed medium workability of the mix, ideal for
general-purpose structural concrete. The experimental flexural strength
results demonstrated that void position significantly impacts beam
performance. Beams with voids located near the supports (especially at
100 mm) performed better than those with centrally placed holes.
Notably, Sample 2 (holes at 100 mm) recorded the highest strength of
3.10 MPA at 28 days, even outperforming the solid control beam,
suggesting that strategic void placement can enhance crack distribution
and strength retention. The water cement ratio is a fundamental
parameter in concrete mix design, define as the ratio of the weight of
water to the weight of cement used in a concrete mixture. The W/C ratio
used is 0.5’ In conclusion, the findings demonstrate that with proper
material selection, adequate curing, and well-engineered void
positioning, hollow reinforced concrete beams can be structurally
efficient and reliable. The study supports their use in practical
applications, particularly in tropical regions like southern Nigeria, and
recommends further exploration through finite element modelling to
refine design strategies.