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. 2022 Feb 17;15(4):1501.
doi: 10.3390/ma15041501.

Effect of Crumb Rubber, Fly Ash, and Nanosilica on the Properties of Self-Compacting Concrete Using Response Surface Methodology

Nurul Izzati Rahim  1 , Bashar S Mohammed  1 , Isyaka Abdulkadir  1   2 , Mohammed Dahim  3
Affiliations

Effect of Crumb Rubber, Fly Ash, and Nanosilica on the Properties of Self-Compacting Concrete Using Response Surface Methodology

Nurul Izzati Rahim et al. Materials (Basel). .

Abstract

Producing high-strength self-compacting concrete (SCC) requires a low water-cement ratio (W/C). Hence, using a superplasticizer is necessary to attain the desired self-compacting properties at a fresh state. The use of low W/C results in very brittle concrete with a low deformation capacity. This research aims to investigate the influence of crumb rubber (CR), fly ash (FA), and nanosilica (NS) on SCC's workability and mechanical properties. Using response surface methodology (RSM), 20 mixes were developed containing different levels and proportions of FA (10-40% replacement of cement), CR (5-15% replacement of fine aggregate), and NS (0-4% addition) as the input variables. The workability was assessed through the slump flow, T500, L-box, and V-funnel tests following the guidelines of EFNARC 2005. The compressive, flexural, and tensile strengths were determined at 28 days and considered as the responses for the response surface methodology (RSM) analyses. The results revealed that the workability properties were increased with an increase in FA but decreased with CR replacement and the addition of NS. The pore-refining effect and pozzolanic reactivity of the FA and NS increased the strengths of the composite. Conversely, the strength is negatively affected by an increase in CR, however ductility and deformation capacity were significantly enhanced. Response surface models of the mechanical strengths were developed and validated using ANOVA and have high R2 values of 86-99%. The optimization result produced 36.38%, 4.08%, and 1.0% for the optimum FA, CR, and NS replacement levels at a desirability value of 60%.

Keywords: crumb rubber (CR); nanosilica (NS); response surface methodology (RSM); self-compacting concrete (SCC).

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Conflict of interest statement

The authors declare that there is no conflict of interest.

Figures

Figure 1
Figure 1
(a) Grading of aggregates and CR; (b) XRD pattern of nanosilica.
Figure 2
Figure 2
The materials used as the RSM input factors. (a) class fly ash; (b) crumb rubber, and (c) nanosilica.
Figure 3
Figure 3
(a) T500 and (b) slump flow (dmax).
Figure 4
Figure 4
(a) L-box (passing ability) and (b) V-funnel.
Figure 5
Figure 5
Slump flow for (a) mix FA25CR7.5NS0 and (b) mix FA10CR15NS0.
Figure 6
Figure 6
Compressive strength of RSCC mixes at 28 days.
Figure 7
Figure 7
(a) FA40CR0NS4 sample at failure; (b) FA40CR15NS4 sample at failure.
Figure 8
Figure 8
Flexural strength result at 28 days.
Figure 9
Figure 9
Stress-deflection curve for flexural test.
Figure 10
Figure 10
Tensile strength of RSCC mixes at 28 days.
Figure 11
Figure 11
(a) Formation of primary and secondary hydration products due to FA and NS. (b) Presence of voids and microcracks in a mix having CR.
Figure 12
Figure 12
(a) Normal plot of residuals and (b) predicted versus actual plot for compressive strength.
Figure 13
Figure 13
(a) Normal plot of residuals and (b) predicted versus actual plot for flexural strength.
Figure 14
Figure 14
(a) Normal plot of residuals and (b) predicted versus actual plot for tensile strength.
Figure 15
Figure 15
(a) 2D contour plot and (b) 3D response surface diagram for CS.
Figure 16
Figure 16
(a) 2D contour plot and (b) 3D response surface diagram for FS.
Figure 17
Figure 17
(a) 2D contour plot and (b) 3D response surface diagram for TS.
Figure 18
Figure 18
Optimization solution ramp.
Figure 19
Figure 19
3D response surface diagram for the desirability of the optimization.
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