This high water-cement ratio affects the hydration reaction by producing a porous network of Calcium Hydroxide and Ettringite. The film of water causes a relatively high-water cement ratio in the vicinity of the aggregates. When concrete is prepared, the water present in the mix forms a film around the aggregate. The interfacial transition zone exists between the coarse aggregates and the mortar. It is due to the Interfacial transition zone. The goal is for the concrete mixture to be homogeneous throughout the structure.Īs the course aggregate size increases, the compressive stress decreases. If the aggregate cannot get around the reinforcement, you will have segregation with just mortar and no aggregate in spots where the aggregate can’t get through. The size of the aggregate is very important when you have reinforcement. You need to have some voids though, because the chemical stabilization comes from the cement mortar. * percent air voids in loosely compacted aggregates smaller than 2.36 mm * ensures a high degree of fine aggregate internal friction and rutting resistance * percent by weight of agg’s larger than 4.75 mm with one or more fractured faces * ensures a high degree of internal friction and rutting resistance The slide below is discussing fractured faces in asphalt concrete, but the characteristics are similar in concrete. This, in combination with having a good percentage of fractured faces on the rock, tend to mechanically strengthen the concrete. The combined gradation is closer to the well graded mix, but it is still a little different. The picture below shows a well graded, poorly graded and gap graded mix. Research today shows that a combined gradation where there is not a lot of voids seems to provide a stronger stone matrix. This actually goes against some of today’s research. Where it was not delaminated, it was tough to demolish. The concrete on the bridge was very strong, but not lasting all that long. I worked on a bridge several years ago where there was a lot of river rock in it. The coarse agg size is not as much of a factor as the gradation of sizes of agg, the shape of the agg, and the strength of the agg.
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