Babatunde J Olawuyi

(CSSA), member of both fib and RILEM and currently serves in the RILEM TC 260-RCS. His research interests cover cementitious materials, concrete, fibre reinforced concrete and sustainable development. ABSTRACT Superabsorbent polymer (SAP) addition as an internal curing (IC) agent in high-performance concrete (HPC) has been adjudged to be effective in mitigating autogenous shrinkage. The influence of SAP created voids fresh properties and early strength development of the HPC as cement hydrates is however yet to be well understood. This paper hereby presents a report of an experimental study on SAP incorporation as an internal curing agent in a low water/binder (W/B) HPC. Four reference HPC mixtures (M1F, M1S, M2 and M3) designed for a 28-day minimum cube compressive strength of 70 N/mm 2 (MPa) were examined for the effect of SAP grain size, content and binder type on setting times and degree of hydration. The study also involved the determination of the pH-value of the simulated cement pore solution obtained from the binder combination types and its influence on SAP absorbency in concrete. It was observed that the addition of SAP resulted to increase in the setting times, while the degree of hydration of the HPC mixtures was found to increase as SAP content increases. The higher the SAP grain size, content and W/B for all mixtures, the higher the chemically bound water () at specific times and this increased as the hydration period increases. INTRODUCTION The incorporation of superabsorbent polymers (SAP) in concrete is gaining acceptance as an internal curing (IC) agent especially in high-performance and ultra-high performance concrete. However, the effect of its utilisation on cement hydration and strength development in these types of concrete is yet to be fully understood. Amongst the issues of concern is the effect of SAP on the fresh properties of concrete such as workability, setting times and rate of hydration. Also, the influence of the cement pore solution (CPS) concentration on the rate of fluid absorption and

Incorporating Superabsorbents Polymers (SAP) as internal curing agents (IC-agents) in high performance concrete (HPC) for mitigation of autogenous shrinkage is one new trend in concrete practice. SAP's water absorption and desorption as cement hydrates however leaves micro voids within the concrete which can negatively influence the mechanical properties of HPC. The SAP content, sizes, binder composition, solid constituents of concrete and curing age could be of direct influence on the resultant air voids sizes and its distribution in concrete. This paper therefore reports on three dimensional (3D) volume analysis of the influence of SAP contents and curing age on air voids distribution in HPC. Four HPC mixtures with different binder constituents and water/binder (W/B): M 1F and M 1S (0.2), M 2 (0.25) and M 3 (0.3) were tested with two grain sizes of SAP (SP 1 6 300 lm and SP 2 6 600 lm). The SAP contents were also varied (0%; 0.2%; 0.3%; and 0.4%) by weight of binder. Concrete cylinders (50 mm b  100 mm) were cast and cured in water for different ages (7, 28, 56 and 90 days) before the hardened HPC was subjected to X-ray computed tomography (CT) scanning for determination of the air void distribution. The analysed 3D X-ray images gave results on SAP grain sizes, SAP air voids, distribution and volume in the HPC with the respective influence of binder type, W/B and curing age assessed.

X-ray computed tomography is a well-known technique to measure porosity in materials such as concrete, though this usually involves time consuming scans and complex analysis procedures. Many of these involve custom software or programming procedures. In this paper, a simplified procedure is presented and demonstrated using results obtained from basic procedures with commercial software packages, with minimal image processing. The same sample was subjected to scans ranging from 100 μm to 5 μm resolutions, demonstrating the multiscale ability of commercial CT scanners. Scans done at typical high-quality conditions (1 hr duration) in comparison to very fast scans (5 minutes) are also presented and it is demonstrated that useful information is still obtained from such lower quality faster scans. This demonstrates the concept that X-ray CT is simple and cost effective for research and industrial applications, not requiring expert 3D image analysis experience, for obtaining good porosity information.

The use of Superabsorbent Polymers (SAP) is one internal curing method being adopted for mitigation of autogenous shrinkage in concrete especially high strength / performance concrete (HSC/HPC). SAP absorbs water and release the water internally when concrete hydrates. It however leaves micro voids in this process; this can negatively influence the mechanical properties of concrete. This paper therefore reports on three dimensional (3D) volume analyses of the air voids in HPC containing SAP as internal curing agent. Three HPC mixtures with different water/binder (w/b) ratios (M1 (0.2); M2 (0.25) and M3 (0.3)) were tested with two grain sizes of SAP (˂ 300 µm with product label FLOSET CS 27 and ˂ 600 µm, labelled FLOSET CC 27). The SAP contents were also varied (0%; 0.2%; 0.3%; and 0.4% by weight of binder). Concrete cylinders with 50 mm in diameter and 100mm in height were cast and cured in water for 28 days before the dry hardened HPC was subjected to X-ray computed tomography (CT) scanning for determination of the air void distribution. The 3D X-ray images were then examined and analysed using Avizo Fire image analysis software – version 8.0 to filter and classify the individual voids for determination of the sizes, distribution and volume analysis of void created by SAP in the HPC with the respective influence of binder type and water/binder ratio assessed. The CT scanning was also used to affirm the grain sizes of the dry SAP and their absorption in pore solutions.

This work involved onsite observation of the production process; determination of physical properties and chemical composition of the soil sample used for production of Makurdi burnt bricks (MBB). A total of 22 brick specimens, of the MBB was examined in the laboratory for compressive strength, water absorption and abrasion resistance. The results reveal the soil sample as a true laterite having a Silica-Sesquioxide ratio of 1.01, Silica content of 42.95 and  clay content of 27.38 and total clay + silt content of 30.78. The Atterberg’s limit test gave the liquid limit as 36.79; plastic limit, 26.11and plastic index, 10.68.  Compressive strength was 3.46 N/mm2 and 11.75 N/mm2 for Samples A and B respectively; Average water absorption for Sample B (16.49%) was double that of Sample A (8.58%) while the Abrasion resistance ability of Sample B (33.67%) was four times better than Sample A (9.32%).