Precast News From China
With the promotion of year-round operations in the construction industry, winter construction has become increasingly common.
However, whenever the temperature drops sharply, the core challenge faced by construction is whether pouring concrete in cold winter weather is feasible?.
As a key indicator for engineering quality control and acceptance, concrete strength naturally attracts the attention of technical personnel and construction units in concrete enterprises.
In concrete production and engineering practice, there is often a phenomenon of “early stage deformity, later stage defects”, that is, the early strength of concrete is higher at 7 days, and the strength growth is slow after 28 days.
Excessive early strength growth not only inhibits later strength improvement, but also increases the difficulty of controlling concrete cracks due to high hydration rate and heat of hydration, thereby adversely affecting the durability of concrete.
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After decades of development, both the mix proportion and production process of concrete are relatively mature.
However, the uneven quality and frequent fluctuations of raw materials, as well as the frequent occurrence of concrete quality problems caused by untimely or inadequate adjustment of concrete mix proportion, are the current difficulties in concrete quality control.
For example, the phenomenon of pipe blockage caused by poor aggregate wrapping, segregation, bleeding, or significant loss of slump over time in concrete mixtures is rampant.
The problem of unqualified engineering quality caused by fluctuations in raw materials, such as insufficient strength of concrete test blocks to meet design requirements or large strength dispersion, is not uncommon.
With the increasing efforts in environmental protection, unstable raw material quality has become the norm.
Understanding the current status of concrete raw materials, adapting concrete production to fluctuations in raw material properties, and improving concrete quality are of great significance.
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(Overview: This article is relatively long and boring, but it is of practical help to those who want to quickly understand the European standard system.
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In low strength grade concrete, the amount of cementitious material used is small, and the amount of slurry is also small.
Increasing the particle size of the aggregate appropriately and reducing the specific surface area can reduce the amount of slurry used, increase the compactness of the concrete, and improve its strength.
But it’s not that the larger the particle size, the higher the concrete strength.
In high-strength concrete, the larger the particle size of the aggregate, the higher the probability of defects.
In concrete mixtures, the larger the particle size of the aggregate, the faster it sinks, resulting in poor uniformity and low strength of the concrete.
The use of small-sized aggregates in high-strength concrete can reduce aggregate defects, increase the bonding area between aggregates and cement slurry, and improve concrete strength.
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In engineering practice, on the one hand, the compressive strength of test blocks under the same conditions is used as the basis for demoulding, and on the other hand, it is based on the fact that demoulding after concrete setting does not affect the appearance quality of the concrete, such as not sticking to the mold, falling corners, etc.
However, in practical engineering, the sampling and production of test blocks are not standardized, resulting in a widespread phenomenon of arbitrary demoulding, which poses hidden dangers to engineering quality and construction safety.
Premature demoulding can cause damage to the appearance of concrete, while severe cases can result in cracks.
In severe cases, it can cause structural collapse and lead to major quality accidents.
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After cement hydration, a large amount of Ca (OH) 2 will be generated.
Except for a small amount dissolved in the pore fluid, which makes the concrete alkaline, most of it exists in a crystalline state and becomes a reserve for the pore fluid to maintain high alkalinity.
CO2 gas in the air continuously passes through the coarse capillary channels in the concrete that are not fully filled with water, and neutralizes the Ca (OH) 2 dissolved in the pore fluid.
The reaction generates CaCO3 and H2O that are insoluble in water.
CaCO3 adheres to the surface pores, increasing the density of the concrete surface and thus improving the strength of the surface concrete.
However, the internal strength does not increase, so the depth of carbonation needs to be measured and corrected.
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The additive industry has undergone decades of development, and in addition to traditional additives such as water reducers, retarders, and early strength additives that can have intuitive effects, they can continue to develop.
However, additives such as expansion agents, rust inhibitors, anti crack fibers, etc.
have gradually lost credibility.
It is not due to problems with the additive products, but rather due to human factors and market factors that more and more construction sites have doubts about the effectiveness of the additives and have abandoned them.
There are various reasons for this, including counterfeiting and non necessity.
The main reasons are as follows:.
In the field of municipal and environmental engineering, the efficient construction of underground space cannot be separated from the innovation of key infrastructure.
Yatai Building Materials, with the core concept of “Thai Chain Intelligent Manufacturing”, has launched precast concrete shafts to provide environmentally friendly, safe, and efficient solutions for underground spaces and ground communication channels.
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Ruida Heng Research Institute focuses on industry research reports in the engineering field, as well as research and interpretation of real-time industry trends and national industrial policies, providing professional third-party perspectives and accurate market analysis for engineering industry clients.
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