The slump of fresh concrete is relatively small and the expansion degree is smaller, while the amount of water reducing agent used at this time is commonly referred to as “unable to open”; 2.

These data can help us choose the type of retarder.

The third part of the investigation is to master the variety and fineness of concrete admixtures.

If the mixture is limestone powder during grinding, the finished cement is prone to bleeding.

After the cement is dissolved in water, the alkali content of the solution is the soluble alkali content including the mixture, which may be more meaningful for adjusting the adaptability of the test.

When the mixture is made of pozzolanic materials such as coal gangue, shale ash, zeolite, etc., the finished cement behaves as an absorbent high efficiency water reducing agent.

The slump loss is large, and sometimes there is even a false set, that is, the cement slurry is very thin at the beginning of mixing, and then quickly becomes sticky and dry.

When grinding clinker, if the mixture is only slag (water slag) or fly ash, the adaptability of the finished cement to external additives, especially retarders, is good.

This is very unrealistic for pumping agents with a normal dosage of less than 2.5% to achieve a saturation content, and even “close” is impossible.

The second part of the investigation is to understand what types of mixing materials are added and how much is added when clinker is ground into cement, which is very helpful for analyzing the causes of abnormal (too long, too short) concrete bleeding and setting time.

Incompatibility between admixtures and cement often occurs, especially when pumping water reducing agents are used.

Generally, the pH value should be above 12, but there are also ordinary Portland cement with a pH value of only 9-10, and some of them are lower.

The cement paste test can be conducted using pure cement, or the total amount of cementitious material of 300 grams can be distributed according to the proportion of cementitious material in the concrete mix proportion.
.

Take a drop of the clear liquid and place it on a wide pH test paper.

The amount of water reducing agent must be increased significantly to obtain the expected concrete slump, and the expansion may not meet the requirements, often at the expense of the amount of additive, and the effect is not obvious.

The loss on ignition of fly ash and the amount of stone powder added to slag powder (in colloquial terms, the degree of adulteration) are important, which directly affect the adaptability of admixtures, especially high-efficiency water reducing agents and retarders, to cement.

Fully mixed with slag powder is prone to bleeding, but it improves various properties of concrete.

Step 3: Find out the saturated content value of the high efficiency water reducing agent used for this cement.

However, the saturation content point of early strength cement is generally high, resulting in a traditional high efficiency water reducing agent dosage of more than 1% or 0.8% (calculated based on the converted solid content).

The minerals that affect the adaptability of cement are C3A, C3S, and C4AF.

The test results can preliminarily determine whether the soluble alkali content in cement is large or small; Whether the mixture in the cement contains slightly acidic materials or inert materials such as stone powder, resulting in a low pH value.

The gypsum added during clinker grinding also has a significant relationship, such as desulfurization gypsum, anhydrite, insoluble anhydrite, industrial waste gypsum, titanium gypsum, etc., which have significant differences in the adaptability of cement and additives.

One part of cement (by weight) can be dissolved in three parts of water, fully stirred, and precipitated to clarify.

The reasons for the incompatibility between specific admixtures and specific cement may come from three aspects: cement properties; Concrete composition materials, especially sand and admixtures; The admixture itself does not match properly.

Mortar cannot wrap the stones, causing segregation but not significant bleeding; 5.

It mainly depends on the combination of different high efficiency water reducing agents and multiple retarders to achieve the purpose of adjusting adaptability.

Although the amount of other industrial waste slag added may be small, the adaptability of ground cement to additives is poor, and it is relatively difficult to adjust.

This is like asking, smelling, looking, and cutting in traditional Chinese medicine.

The manifestations of incompatibility are generally as follows: 1.

The closer the dosage of high efficiency water reducing agent is to the saturated content of the cement, the easier it is to obtain better adaptability.

If two or more high efficiency water reducing agents are mixed, find out the saturated content point through the cement paste test based on the total amount of mixed.

In short, diagnosis should be made before a treatment plan can be formulated.

Lifting Insert

Step 2 of the test: The first part of the investigation is to obtain the clinker analysis results of this cement.

Calculate the content of four minerals in cement: tricalcium aluminate C3A, tetracalcium ferroaluminate C4AF, tricalcium silicate C3S, and dicalcium silicate C2S.

The first step of the test is to detect the alkalinity of the cement and determine the pH value of the cement to be used, using a pH meter, pH meter, or pH pen.

The fineness of the admixture is crucial, as its coarseness not only causes bleeding in the concrete (such as coarse fly ash), but also increases the slump loss.

Observe the degree of discoloration on the back of the test paper to determine the alkalinity of the cement.

Full mixing of ordinary fly ash requires more mixing water and has a long setting time, but it significantly inhibits bleeding.

However, cement using water quenched granulated blast furnace slag as the mixture sometimes dries because its hardness is greater than that of the clinker and it is not easy to grind to the same fineness as the clinker.

If mixed with unified fly ash, due to a portion of tertiary ash, it is often the main reason for the “failure” of high-efficiency water reducing agent.

In addition, based on the alkali and sulfur content data in the clinker analysis, the plasticity value SD can be calculated as a reference basis for appropriately adding sulfate or alkali when mixing admixtures.

Which one is the main reason needs to be tested and analyzed.

No obvious discomfort was observed in the fresh concrete, but the strength after hardening was low.

However, high-quality fly ash can reduce the amount of water reducing agent.

According to experience, the dosage of water reducing agent is lower than 70% of the saturated dosage, even if multiple retarders are used to adjust the adaptability simultaneously, satisfactory results cannot be obtained.

After being discharged from the machine, the workability of the concrete is very poor; Although the slump and expansion are not small, the concrete bleeding sometimes lags behind for 1 to 3 hours and has a large amount; 4.

Although the alkali content in the clinker analysis sheet is the total alkali content rather than the pure soluble alkali content, it still has important reference value for quickly determining the SD value.