Study of water intrusion in admixture concrete using neutron backscattering technique

This work aims to study the water infiltration in ordinary concrete with different percentages of super-plasticizer (SP) varied from 0.25% to 1.5% of cement weight. It was performed by measuring thermal neutrons backscattered from the investigated samples. Dynamic measurements were carried out by fixing the sample on a transfer table in front of the neutron beam exit. A slit collimated beam of neutrons emitted from ²⁵²Cf was hit on which surface of the sample water did not infiltrate through it and along the flow direction. Further, static measurements were made using collimated neutron beams of thermal and fast neutrons emitted from sources of ²⁵²Cf and Pu-Be with strength of 1.3 × 107 and 5 × 10⁶ n/s respectively. These beams of neutron incident on the other side of sample which water allowed infiltrating for 7, 14, 21, 28, and 35 days. The backscattered thermal neutrons were measured by BF3 detector which fixed on the same side of the incident neutron beam. The obtained results show clearly the dependence of water infiltration on the percentages of SP and the submerged time. As well as, the measuring sensitivity depends on the main energy of the incident neutrons, submerged time, and SP% was given and discussed. The results indicated that samples with SP below 1.5% show an improvement in resistivity to water infiltration and therefore prolong the concrete durability for marine constructions. The best percentage of SP is 1%, for more percentages, there is a negative effect on the permeability and diffusivity. As well as, the obtained results indicated that, NBS is a powerful, nondestructive, and fast method to observe water infiltration in porous materials. In addition, these results lead to improve concrete properties to prevent fluid intrusion. Further investigation should be done with different recycled additives to achieving the optimization between waste reuse and engineering properties of porous concrete.