Due to the use of mineral admixtures, High Performance Concrete has a lower water-cement ratio and better particle distribution than CCC, resulting in much fewer porosity per unit volume of cementitious materials in the mixture. The hydration product filling of voids in HPC is substantially faster than in conventional concrete because smaller pores require fewer hydration products to fill. As a result, moisture loss due to capillary action in HPC stops sooner than in CCC under the same curing conditions.
HPC has been found to lose the most moisture in the first 24 hours. The early stage hydration rate of HPC is higher than traditional concrete because to the low water-cement ratio and usage of superplasticizer, resulting in reduced long-term hydration.
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Curing of High Strength Concrete
Long-term chloride permeability of HPC containing microsilica or fly ash has been found to be unaffected by curing time after the first moisture protection. All of this suggests that when compared to CCC, HPC requires shorter curing time.bIn contrast to traditional concrete, the length of time spent wet curing has an impact on the shrinkage of HPC. Curing method has a comparable effect on HPC in terms of creep and shrinkage of concrete, which is influenced by the kind and time of curing. Curing is the most difficult aspect of building structures with HPC. When compared to ordinary cement concrete, HPC uses less water for a given level of workability, often even less than the minimum.
As a result, early moisture loss from the concrete has a negative impact on the soundness and long-term qualities of the concrete. As a result, protecting new HPC from moisture loss is critical for the development of strength, the prevention of plastic shrinkage cracks, and durability.Again, early wet curing of HPC is not possible since it will raise the water-binder material ratio near to the exposed surface, causing concrete quality to deteriorate. high-performance-concrete Moisture loss from HPC is greatest during the first 24 hours following installation, according to one study. When compared to CCC, HPC’s fresh concrete mix is more cohesive and has less bleeding.
Methods and Duration of Curing
Because bleed water evaporates quickly, HPC is more susceptible to plastic shrinkage cracks. The first setting period is a critical moment for the formation of plastic shrinkage fractures. As a result, under curing conditions of rising temperature, low humidity, and high winds, which accelerate the evaporation of water from fresh concrete, plastic shrinkage cracks might be a major concern.
To solve this issue, the curing procedure should begin as soon as the fresh HPC is installed. Wet curing, if used shortly after the installation of concrete to prevent plastic shrinkage cracks, as in the case of CCC, would degrade the quality of the hardened concrete’s surface layer.
If wet curing is used before the concrete is fully set, the curing water will dilute the cement paste near the surface, increasing the w/c ratio. As a result, concrete’s strength and impermeability will be severely impaired. As a result, HPC should be cured as soon as possible without using water on the exposed surface of new concrete. This necessitates splitting the HPC curing method into two steps.As a result, HPC is typically cured in two stages: initial curing and wet curing. During the first curing process, no water is used. The start of both stages of curing, as well as their duration, is determined by the concrete’s initial and ultimate setting times.Making a broad specification is tough.
Initial Curing Method for High Performance Concrete
The initial curing is the most difficult component of the HPC curing process. The goal of initial curing is to keep moisture from escaping the fresh concrete until wet curing can begin. The initial curing procedures for HPC are heavily influenced by the construction procedure, exposed surface properties, exposed surface/volume ratio, and climatic conditions.The two types of concrete surfaces that are commonly encountered for curing are Type-1 surface, which is the exposed surface of fresh concrete that will be exposed to the service condition and/or environment after curing, and Type-2 surface, which is the exposed surface of fresh concrete that will be exposed to the service condition and/or environment after curing.This type has a high exposed surface area to volume ratio.Slabs, shell roofs, beams, and other similar structures are examples.
surface – Where concrete beams have a significant depth, such as the IC Dome’s ring beam, etc. The exposed area to volume ratio is smaller on this type of surface. Except for the last one of these segmented pours, the exposed surface of the segmented pours has reinforcement extended for the next pours and to form the construction joints in this situation. To accomplish quality building joints, latent must be removed from the exposed surface.When the ratio of surface area to volume is considered, moisture loss from Type-1 surfaces is often greater than that from Type-2 surfaces.As a result, unique procedures for curing each of these surfaces at the start are critical.
Initial curing for Type-1 surfaces:
For initial curing, the curing chemical has not proven to be highly successful. Water sheen (bleed water) develops on the top of the concrete surface almost immediately after it is poured. Local ponding of the curing compound combined with the water sheen occurs on the concrete surface if the curing compound is spread before the water sheen dries.Allowing the water sheen to entirely evaporate, especially in dry and hot climates, may be damaging to the long-term qualities of concrete. When the curing compound dries out, it forms random-orientation cracks on the membrane generated by the curing compound. These aren’t shrinkage fractures in plastic. The curing ingredient is rendered ineffective in preventing moisture loss because to these fissures.
Initial curing for Type-2 surface :
The following are two extra factors to consider while curing a Type –2 surface for the first time:1) there is reinforcement extending from the exposed surface, and) In order to obtain acceptable quality building joints, the surface must be treated to eliminate the latent for concreting the following pour over it. As with Type-1 surfaces, it is not possible to lay a cover sheet over this type of surface, and the latent on the exposed surface must be removed in order to get proper construction joints. The best way for eliminating the latent from the concrete surface appears to be green cutting.However, it should be done after the final setup time so that the extra water available from the green cutting water-air jet can be used.
The use of a surface retarder can successfully inhibit the production of plastic shrinkage cracks until the final setting of the product. When concrete is covered, moisture loss is reduced, which is visible. In one of the case studies, where M 60 grade HPC was utilised at the Kaiga Nuclear Power Plant in 1998 (Karnataka), the potential for emerging plastic shrinkage fractures was shown to be higher in the finished surface than in the unfinished surface. High Performance Concrete Final Curing Method (Wet Curing)Wet curing, such as ponding water on the exposed surface or covering the exposed surface with wet burlap and keeping it wet with continual sprinkling of water, has been proven to be helpful for ultimate curing.
Curing Duration for High Performance Concrete
The initial curing of HPC should begin immediately after the laying of new concrete and continue until the concrete has reached its final setting point. It could be a better idea to extend it for around an hour after the final setup time. Wet curing comes after the initial curing. The total curing time for HPC is the sum of the initial curing time and the wet curing time, with the second component being the longer.Curing method has a comparable effect on HPC in terms of creep and shrinkage of concrete, which is influenced by the kind and time of curing. In light of the foregoing, a curing time of 7 to 10 days appears to be required for HPC, while a time of 1-2 days may suffice.
Concrete typically takes 24 to 48 hours to dry enough for you to walk or drive on it.
The period can be reduced to 3 days if high early strength concrete is used and the temperature.
Cure time is the time that determines how long things take to fully cure.