Segregation sensitivity of concrete

Abstract

Concrete segregation is a significant problem associated with concrete that can affect concrete in different phases starting from concrete matrix to compaction. Concrete segregation directly affects the compressive strength and different mechanical & physical properties, such as tensile strength, elastic properties, shrinkage, creep, & cracking resistance, of the structure, eventually decreasing its strength & service life. The researchers are still yet able to find out the methods that talk about the stability of a concrete structure w.r.t segregation, but quantification of the segregation is an issue still under-studied.

This study estimates sensitivity to the segregation of different concrete samples with slump classes ranging from S2, S3, S4, to S5. During the study, a total of 9 concrete mixes, compacted at 25-seconds & 50-seconds, were used in 3 different series such as variable Superplasticizer (SP), water-to-cement ratio (w/c), & Air-entraining agent (AEA), respectively. The preliminary estimation of the segregation sensitivity of concrete samples was done via Individual Discs Density comparison & Visual Inspection of vertical cut sections. Moreover, the Air porosity was calculated using the Pressure Saturation (PS) test & Suction porosities were obtained through Capillary Suction (CS) testing method. The ratio difference in the air-to-suction porosity provides us with Air segregation of the testing samples. Furthermore, the difference in the percentage share of cement paste & aggregate in the top, middle, & bottom discs help us to estimate cement paste segregation & aggregate segregation, respectively. The researchers have been combining different methods to calculate the cement paste, aggregate & air segregation of the concrete sample but the Pressure saturation & Capillary suction tests enable us to estimate all three types simultaneously.

The statistical analysis of the results of the slump classes used during the thesis work shows that the concrete samples with the S2 slump class are less sensitive to all types of segregation, whereas S4, & S5 are more sensitive to segregation. However, the S3 slump class concrete shows a dual behavior. It depicts a higher sensitivity to segregation if prepared with a higher Superplasticizer (SP) or Air-entraining agent (AEA) at a higher compaction time, but it is less sensitive to segregation if prepared with zero AEA or higher w/c ratio.