The Use of Blended Cinder Aggregates for Concrete Mixes

Abstract

The study to design concrete by using cinder blended aggregates was conducted in Mbeya Region Tanzania. Cinder aggregates were blended with crushed stones aggregates for concrete mixes. In Mbeya Region there are abundant volcanic materials which are pozzolan, cinders and pumices. The study involved characterization of source aggregates and for blended aggregates. The materials used for this study were natural cinder aggregates from Ituha, Crushed stone aggregates from Mbalizi and excavated pit sands from Ituha. The binder used was CEMI 32.5N manufactured by Tembo Lafarge Cement Company Limited.

The results from strength and physical properties tests of aggregates indicated that Ituha cinder aggregates have low strength, low specific gravity and high water absorption compared to Mbalizi crushed stone aggregates. The strength results for Ituha cinder aggregates are 75kN for TFV, 38.76% for ACV and 48. 26% for AIV. The results of SG, WA, EI and FI for Ituha cinder aggregates are 1.77, 3.31%, 19.82% and 12.88% respectively. The strength results for Mbalizi crushed stones aggregates are 240kN for TFV, 15.82% for ACV and 18. 30% for AIV. The results of SG, WA, EI and FI for Mbalizi crushed stone aggregates are 2.63, 0.87%, 34.41% and 12.60% respectively. The SG and WA for Ituha pit sand are 2.44 and 3.18% respectively.

Sieve analysis for Ituha cinder aggregates, Mbalizi crushed stone aggregates and Ituha pit sands were conducted. The aggregates and sands were blended together to get six blended sample materials targeting the selected aggregate envelopes for concrete mixes. The concrete were prepared for two different cement contents of 350kg/m³ and 450kg/m³ mixed at W/C ratio of 0.55. Due to high demand of mixing water the super plasticizer at 2.5% and 3% for cement content of 450kg/m³ and 350kg/m³ respectively were added to fresh concrete. The concretes were cured under water for 7days, 14days, 21days and 28days. The results for compressive strength indicated that the compressive strengths increased with increasing curing period and increased amount of Mbalizi crushed aggregates and cement contents. The compressive strength of concrete specimens mixed at cement content of 350kg/m³ cured for 28days are 23.8MPa for 55IPS45MCA00ICA, 22.3MPa for 50IPS36MCA14ICA, 20.7MPa for 45IPS27MCA28ICA, 18.4MPa for 40IPS18MCA42ICA, 18.0MPa for 35IPS09MCA56ICA and 16.6MPa for 30IPS00MCA70ICA. The compressive strength of concrete mixed at cement content of 450kg/m³ cured for 28days are 27.8MPa for 55IPS45MCA00ICA, 29.0MPa for 50IPS36MCA14ICA, 26.1MPa for 45IPS27MCA28ICA, 24.6MPa for 40IPS18MCA42ICA, 22.9MPa for 35IPS09MCA56ICA and 22.2MPa for 30IPS00MCA70ICA. But also densities of cured concrete specimens for both cement contents increased with increased curing periods and amount of Mbalizi crushed aggregates. The increase in compressive strength with increased curing period and Mbalizi crushed aggregates is because of development of cementitious compound and high resistance against crushing. For this study for easy blending process of aggregate materials, the blending model have been developed, the model uses median particle size (MS) and grading factor (GF) as variables. To make use of strength of aggregate materials, the prediction model of compressive strength of 28days cured concrete specimens was developed. The model uses TFV, SG and cement content as variables.