Ifyouarenew to theconcreteindustry,thenherearethreechangesyouneedtopayspecialattentiontoafterconcreteconstruction. This may be just abrief introduction,but if you need further study,you can consult the relevant information on your own and continue to follow up on the relevant research progress we have published.By the way,Concrete admixturesareagoodhelpandimprovementforthesechanges.
1. Slump
Slump is a method and indicator for measuring the workability of concrete. On construction sites and in laboratories, slump tests are typically performed to determine the fluidity of the mixture, supplemented by intuitive assessments of cohesiveness and water retention. Slump is a quantitative indicator used to measure the degree of workability and to determine whether construction can proceed normally.
(1) Methods for detecting slump
A slump cone, shaped like a trumpet with a top opening of 100mm, a bottom opening of 200mm, and a height of 300mm, is used to pour concrete in three stages. After each filling, a tamping hammer is used to evenly tap the cone 25 times from the outside in , compacting the concrete and smoothing it. Then, the cone is lifted, and the concrete slumps due to its own weight . The slump is calculated by subtracting the height of the highest point of the slumped concrete from the height of the cone (300mm). If the difference is 10mm, the slump is 10.
(2) Slump loss rate
Slumpcanchangeovertime. For example: if the slump of freshly mixed concrete is 200 after sampling, but the actual slump of the concrete delivered to the construction site is 150, then the slump is 50 centimeters less than the 200-150. This is the slump loss. AddinganappropriateamountofPolycarboxylicSuperplasticizer(PCE)canreduce the slumplosswithin a certainperiod of time.
2.Bleeding
This refers to the upward movement of water in concrete before it has set, even though the concrete volume is fixed. This is mainly caused by the fact that the aggregate particles in the freshly mixed concrete cannot absorb all the mixing water.Fortheproblemofconcretebleeding,PCE areused to compoundspecialwaterbleedinginhibitorsorthickeners(suchascelluloseether),whichcanincreasethecohesionoftheslurrywhileensuringfluidityandpreventingwaterfromfloating.MineraladmixturessuchasMicrosilicacanalsobeadded,andtheirfineparticlescanfillvoidsandlockinmoisture,radicallyreducingbleedingandimprovingcompactness.
3. Segregation
Segregation in concrete occurs when the cohesion between the components of a concrete mix is insufficient to resist the settling of coarse aggregates, causing the concrete mix components to separate and resulting in uneven internal composition and structure. This typically manifests as the separation of coarse aggregates from the mortar, for example, denser particles settling at the bottom of the mix, or the coarse aggregates separating entirely from the mix. Microsilica mentioned above is also one of the important admixtures to prevent concrete segregation.
(1) Reasons for segregation
Segregation may be caused by improper casting or vibration, excessively large maximum aggregate size, excessively high proportion of coarse aggregate, low content of cementitious materials and fine aggregate, excessively high density of coarse aggregate compared to fine aggregate, or an mixture that is too dry or too thin. Using mineral admixtures or air-entraining agents can reduce the tendency to segregate.
(2) The dangers of segregation
- It affects the pumping performance of concrete, causing issues such as sticking to the pump, pipe blockage, and delays in construction, thus reducing economic benefits.
- This affects the appearance of the concrete structure, causing phenomena such as sand marks, exposed aggregate, and exposed reinforcing bars on the concrete surface.
- This significantly reduces the strength of concrete, severely impacting the load-bearing capacity of the concrete structure, compromising the safety performance of the structure, and in severe cases, causing rework and huge economic losses.
-The poor homogeneity of concrete leads to uneven shrinkage in different parts, making it prone to shrinkage cracks. This is especially true during the construction of concrete slabs, where segregation causes a thickening of the surface cement paste layer, resulting in a sharp increase in shrinkage and severe cracking. This significantly reduces the concrete's durability properties, such as its impermeability and frost resistance.
