Author: Mitchel Anthony
Publisher:
Published: 2022
Total Pages: 0
ISBN-13:
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Self-Consolidating Concrete (SCC) is a highly flowable form of concrete that can fill formwork without mechanical consolidation or segregation. Self-Consolidating Concrete has gained popularity in recent times due its high workability. The high workability of Self-Consolidating Concrete is primarily achieved with the inclusion of a High-Range Water Reducing Admixture (HRWRA) within the material matrix. The inclusion of an HRWRA provides high workability, yet avoids material segregation. Self-Consolidating Concrete workability is measured by the ASTM C1621 J-Ring flow test which measures the spread diameter of the fresh concrete from an inverted mold. Project requirements may also require Self-Consolidating Concrete to achieve high strength. The inclusion of an HRWRA allows the concrete mix to have a lesser water-to-cement ratio, thus increasing the compressive strength of the mix. An additional method to achieve high strength is to incorporate a supplementary cementitious material within the material matrix, with Metakaolin being one of the more common supplementary cementitious materials. A potential supplementary cementitious alternative to Metakaolin is Pumice. The primary focus of the experimental research is to evaluate the effectiveness of pumice as a supplementary cementitious material within high performance Self-Consolidating Concrete. Two grades of supplementary cementitious Pumice (Hess NCS-3 and Hess NDS325) were evaluated during the experimental testing, which were compared against Metakaolin and conventional Self-Consolidating Concrete. The experimental research was conducted in three phases with a primary focus on workability, 7-day, and 28-day compressive strength testing. Secondary testing (air content and tensile testing) was conducted during Phase II to acquire additional attributes of each Self-Consolidating Concrete mix. Phase I testing was performed on Pumice, Metakaolin, and conventional Self-Consolidating mortar cubes to develop preliminary mix designs for each alternative. The primary target for Phase I testing was to develop the appropriate cement quantity to be replaced by the supplementary cementitious material. Testing was conducted on 0%, 5%, 10%, and 15% replacement alternatives within each mix design. Phase II testing was then conducted using Self-Consolidating Concrete cylinders and used the preliminary Phase I mix designs as a reference. The primary focus of Phase II testing was to refine the preliminary mix designs and evaluate each Pumice grade's effectiveness as a supplementary cementitious material. Only the better performing Pumice grade was incorporated into Phase III testing. The intent of Phase III testing was to refine the Phase II mix designs, and make final a recommendation on the effectiveness of Pumice as supplementary cementitious material while using the refined Metakaolin mix designs as a datum. Phase I testing determined that 15% cement replacement was most effective for Metakaolin, NCS-3 Pumice, and NDS325 Pumice. The mortar mix design with 15% Metakaolin replacement provided an average 28-day compressive strength of 10,156 psi, whereas NCS-3 and NDS325 Pumice provided a strength of 6,491 psi, and 5,575 psi respectively. Phase II testing concluded that NCS-3 was the better performing supplementary cementitious Pumice grade with an average 28-day Self-Consolidating Concrete cylinder compressive strength of 9,779 psi compared to NDS325's 7,813 psi compressive strength. Phase III testing concluded that Self-Consolidating Concrete mixes using Metakaolin as a supplementary cementitious material provided the highest 28-day average compressive strength at 11,206 psi. NCS-3 Pumice was competitive with the highest 28-day average compressive strength of 11,067 psi. Metakaolin, however, well outperformed NCS-3 Pumice during 7-day compressive strength testing with average highs of 10,836 psi, and 8,812 psi respectively. Workability testing completed during Phase II and III revealed that Self-Consolidating Concrete incorporating Pumice outperformed Metakaolin mixes. Based upon the above findings, it was concluded that NCS-3 Pumice can be used as an effective alternative supplementary cementitious material to Metakaolin for use in high performance Self-Consolidating Concrete.
