# Evaluation of Workability and Mechanical Properties of Bottom Ash Aggregate Concrete
## 5 Conclusions  
In order to use bottom ash, an industrial byproduct, as concrete aggregate, this study experimentally evaluated the effects of the types of fine aggregate and coarse aggregate and \(W\)/C on the mechanical properties of concrete. The results of the experiment show that the density of concrete and the physical properties of aggregate should be considered as important factors for the performance design of concrete containing bottom ash aggregate. In particular, existing studies and databases on the use of bottom ash aggregate are not sufficient, which hinders the establishment of a reliable design standard. The following conclusions can be drawn from the comparison between the present experiment and the existing proposed code equations.  
1. As a result of using bottom ash as fine and coarse aggregates, the initial slump shows a tendency to decrease irrespective of \(W\)/C. The rate of decline in workability was greater when applying the bottom ash as a fine aggregate of particles 600 \(\upmu\)m or less in size than as coarse aggregate.
2. The compressive strength showed a more significant decline when coarse aggregate of large particle sizes was replaced with bottom ash than when replacing fine aggregate. The equation  
Figure 9: Effect of \(\rho_{c}\) on the shear friction strength.  
for predicting the 28-day compressive strength of concrete containing bottom ash (Equation (1)), which was proposed by using important variables such as concrete density, _W_/_C_, and air contents, can be predicted rationally at the level of R\({}^{2}\) = 0.87.
3. When testing the concrete specimens using different types of aggregates, the characteristics of tensile resistance capacity and shear friction strength normalized by compressive strength generally showed a performance improvement with the increase in concrete density. In comparison with the predictive equation of the _fib_ model, the ratios between the predictive values and experimental values were found to be within 0.93-1.01, and so they were generally close to each other.
4. The existing model equation that predicts the modulus of elasticity on the basis of concrete density overestimates the modulus of elasticity in the case of specimens of 1840 kg/m\({}^{3}\) or above. In particular, the effects of the modulus of elasticity of the aggregate (particularly coarse aggregate) on the elasticity modulus of concrete are significant. However, data from mechanical experiments replacing coarse aggregate with bottom ash have been insufficient, and thus, it is necessary to establish a predictive equation of high reliability in the future on the basis of further testing.  
Conceptualization, Y.-H.K. and K.-H.Y.; formal analysis, H.-Y.K. and K.-H.Y.; funding acquisition, Y.-H.K.; investigation, H.-Y.K. and J.-S.H.; project administration, K.-H.Y.; resources, J.-S.H.; supervision, K.-H.Y.; writing--original draft, H.-Y.K.; writing--review and editing, H.-Y.K. All authors have read and agreed to the published version of the manuscript.  
This research project was funded by the Korea South-East Power CO. of South Korea.  
The authors declare no conflict of interest.