Preparation of oil resistant concrete:
In the construction of industrial and civil construction projects, the problem of oil-resistant concrete floors has not been paid enough attention in the past. Generally, only the density of concrete is considered to meet the impermeability requirements. However, due to the influence of construction factors and material quality, even the dense terrazzo surface layer cannot achieve the purpose of oil penetration resistance, and even the cement surface layer is eroded by oil. Therefore, when preparing oil-resistant concrete, it is necessary to consider both the impermeability requirement and the oil-resistant problem, and give consideration to both at the same time.
Oil-resistant concrete is mainly suitable for oil tank engineering, oil-resistant floor, workshop floor, etc. that require high impermeability to store light oil and heavy oil.
There are two main preparation methods for oil-resistant concrete: one is to add an appropriate amount of compacting agent ferric hydroxide to the concrete to produce a glue solution in the concrete to block the capillary channels of the concrete due to water evaporation, thereby further increasing the concrete’s durability. Anti-oil seepage performance; the other is to use the aggregate grading method to greatly increase the compactness of the concrete, so as to achieve the purpose of impervious to oil.
(1) Preparation of oil-resistant concrete by mixing cementing agent
The key to preparing oil-resistant concrete with a compacting agent is to make a qualified iron hydroxide compacting agent. As long as the compacting agent is successfully produced, it can be added to the concrete mixture according to the prescribed ratio and method. There are three ways to make ferric hydroxide.
1. Preparation of Ferric Hydroxide
The production of ferric hydroxide is usually made of ferric chloride and lime paste:
2FeCl₃+3Ca(OH)2→2Fe(OH)3+3CaCl₃
The specific production method is: put a certain amount of ferric chloride in a wooden barrel or a porcelain vat, then filter the lime paste with a 0.6mm sieve, pour it into the ferric chloride solution, and keep stirring until it is evenly mixed. Make it chemically react to become a yellow-brown colloid, and then use indicator paper to identify its alkalinity, so that the pH value is equal to 8.
2. Prepared by chemical reaction method
Prepare the compacting agent ferric hydroxide by chemical reaction method, that is, use ferric chloride processing industry caustic soda (sodium hydroxide) to form:
FeCl+3NaOH→Fe(OH)3+3NaCl
The specific production method is: dissolve industrial caustic soda (NaOH) with 5 times the quality of water, and then gradually pour this solution into the ferric chloride solution, stirring while pouring, until the pH value of the indicator paper is equal to 8. .
3. Preparation by electrolysis method
The electrolysis method is used to prepare the compacting agent iron hydroxide, which is to use the method of anode electrolysis of iron. This method can extract more pure and cheap compacting agent products, which can not only be made into colloidal iron hydroxide with different concentrations, but also can be made into powder for transportation and mixing of concrete.
Engineering experience proves that under normal circumstances, it is more appropriate to add iron hydroxide [Fe(OH)3] compacting agent at 1.5% to 3.0% of the cement mass.
(2) Preparation of oil-resistant concrete by aggregate grading method
The preparation of oil-resistant concrete by the aggregate grading method is to carry out the gradation design of the coarse and fine aggregate through the particle sieving of the coarse and fine aggregate, in order to obtain the concrete with the highest density, thereby improving the oil seepage resistance of the concrete. In essence, this method is the same as preparing water-resistant concrete.
Relevant experts at home and abroad believe that among the many parameters that determine the oil permeability of concrete (mortar), the main ones are the following aspects: the appropriate mass ratio of cement to ore, the adhesion of cement to stone particles, the compactness and Choose the right aggregate.
In the preparation of oil-resistant concrete, the mass ratio of various cements and ores (such as sand crystalline limestone, weathered porous limestone, dolomite, silica, basalt, porphyry and andesite, etc.) is used, and different water-cement ratios and different curing methods are used. Time and method are tested, and the following basic arguments can be drawn: the total area of cement particles must be greater than the sum of the total area of stone particles. If the cement particles surround each stone particle, this concrete (mortar) will not seep oil.
Construction of oil resistant concrete:
The construction quality of oil-resistant concrete has a direct impact on the oil seepage resistance of concrete. Therefore, in the construction process of oil-resistant concrete, the following aspects should be paid attention to.
(1) The raw materials for preparing oil-resistant concrete must comply with relevant national regulations, which is the basis for ensuring the quality of oil-resistant concrete. When preparing concrete, the ingredients should be weighed according to the specified mix ratio, and the water-cement ratio should be more strictly controlled. The total water consumption should deduct the moisture brought in by coarse and fine aggregates and additives (compacting agent and water reducer).
(2) The amount of compacting agent has a key influence on the oil resistance of oil-resistant concrete and oil-resistant mortar. Therefore, the metering of compacting agent should be very accurate. When mixing the compacting agent, the solid content of the colloidal ferric hydroxide should be measured first, and then mixed into the concrete mixing water at a solid content of 1.5% to 2.0% of the cement dosage. When adding compound compacting agent, do not add xylose syrup directly to ferric chloride, but aluminum sulfate (alum) and ferric chloride can be mixed for preparation.
(3) Oil-resistant concrete should not be mixed manually, but should be mixed mechanically, and it is best to use a forced mixer when conditions permit. The time of mechanical mixing is generally 2.5-3.0 minutes to ensure that the concrete is evenly mixed. During the transportation of oil-resistant concrete, stratification and segregation of the concrete mixture should be prevented.
(4) When pouring oil-resistant concrete, unloading should be done evenly, and the coarse aggregate should not be concentrated too much; when vibrating the concrete, attention should be paid to make the vibrating points evenly distributed to prevent leakage vibration, and the concrete must be uniform and dense. After vibrating, attention should be paid to scraping and calendering the surface.
(5) For oil-resistant concrete, more maintenance should be strengthened, and the watering and curing time should be extended appropriately, especially when ferric chloride compacting agent is selected, sufficient attention should be paid. The curing temperature of oil-resistant concrete shall not be lower than 5°C, and the relative humidity shall be greater than or equal to 90%.
Immediately after the concrete is solidified, the surface should be covered with grass curtains, films, or sprayed with curing agent to ensure the early curing degree and prevent capillary cracks on the concrete surface. In order to fully hydrate the cement, the time of watering and curing at room temperature shall not be less than 14 days.
(6) If the oil-resistant concrete structure is underground (such as oil storage tanks, underground oil pools, etc.), effective measures to reduce the groundwater level should be taken in advance according to the actual situation of the groundwater level before construction, so that the concrete can be poured, vibrated and During the maintenance period, it will not be invaded by groundwater.
