Concrete composition materials are generally cement, aggregate, water, mineral admixtures, chemical admixtures. For some concrete with special requirements, some special materials will be added according to the need. It and other commodities, its performance is realized by its raw materials, only control the quality of concrete raw materials, reasonable use of raw materials to obtain excellent performance, low cost concrete.

1, cement
Cement is one of the most important raw materials in concrete, and also an important part to determine the performance of concrete. There are many kinds of cement, Portland cement (P. ⅰ, P. ⅱ), ordinary Portland cement (P.O), slag Portland cement (P.S), volcanic ash Portland cement (P.P), fly ash Portland cement (P.F), composite Portland cement (P.C), aluminate cement, ferric aluminate cement, sulphoaluminate cement and so on. There are two main differences: one is the difference of mineral composition of cement clinker. For example: Portland cement, clinker in silicate minerals; Sulphoaluminate cement, clinker is mainly anhydrous calcium sulphoaluminate mineral. The second is the difference between the variety of mixed materials and the amount of mixing. For example, ordinary Portland cement is mixed with a small amount of active or inactive mixture on the basis of Portland cement, the dosage is 6%~15%; Slag Portland cement is mixed with a certain amount of slag on the basis of Portland cement, the content of 20%~70%; Fly ash Portland cement is based on Portland cement mixed with a certain amount of fly ash, the content of 20%~40%. Due to the different composition, the performance of cement is also different. Different varieties of cement grade grade classification is also different, Portland cement is divided into 42.5, 42.5R, 52.5, 52.5R, 62.5, 62.5R, P.O is divided into 42.5, 42.5R, 52.5, 52.5R, P.S, P.F, P.P, P.C are divided into 32.5, 32.5R, 42.5, 42.5R, 52.5, 52.5R. "R" is to indicate the meaning of early strength type, the number is to indicate that the strength of the cement 28 days is not lower than the strength value of the number. Cement has a shelf life of three months, beyond which cement must be tested to determine whether it is qualified before it is used.

2. Admixtures
Admixtures have now become an indispensable component of commercial concrete, and the application of admixtures in concrete has experienced more than half a century. There are many kinds of admixtures, and their compositions and properties vary greatly. At present, the commonly used admixtures mainly include fly ash, pulverized slag powder, silica powder and zeolite powder.

(1) fly ash: is a kind of industrial waste, is a kind of powdery material collected in the flue of coal-fired thermal power plants. Due to the difference of coal, as well as the different combustion conditions and collection process, the composition and performance of fly ash change greatly. Under the same other conditions, different collection technology has a great influence on the quality of fly ash. The quality of fly ash from air separation is better than that from ball milling. Fly ash is divided into three grades: grade ⅰ, grade ⅱ and grade ⅲ. Grade ⅰ has the best quality. The fineness of grade ⅰ fly ash shall not exceed 12%, water requirement shall not exceed 95%, and burning loss shall not exceed 5%; the fineness of grade ⅱ fly ash shall not exceed 25%, water requirement shall not exceed 105%, and burning loss shall not exceed 8%; the fineness of grade ⅲ fly ash shall not exceed 45%, water requirement shall not exceed 115%, and burning loss shall not exceed 15%. There are three main effects of fly ash on concrete: morphology effect, activity effect and micro-aggregate effect. Is particle size small bead shape effect: fly ash particles, the surface is smooth, so its effect can be summed up in the form filling effect (particle size small, gap filling cement is more dense concrete), surface effect, small size, large specific surface area, the water demand is big, is the negative effect), lubrication (particle size small, spherical particle lubrication. The pulverized fly ash beads are broken and the lubrication effect is reduced. Active effect: refers to the chemical effect produced by the active components of fly ash in concrete. Usually refers to the volcanic ash reaction. The activity effect is reflected in two aspects: one is the pozzolanic reaction ability of fly ash itself; The other is the promotion of mineral hydration process of cement clinker. The pozzolanic reaction of fly ash should absorb Ca (OH) 2 (calcium hydroxide) generated by the reaction of cement clinker, so as to accelerate the reaction of cement clinker and develop the strength of concrete well. Micro aggregate effect: due to the fine particles of fly ash evenly distributed in the base phase of cement slurry, just like the fine aggregate. The hardened slurry can be regarded as "micro concrete". The glass beads of fly ash have high strength and are well dispersed in the slurry, so they can enhance the structural strength of hardened slurry and improve the strength of concrete.

②, ground slag powder (referred to as: ore powder) : refers to the blast furnace slag formed by water quenching and rapid cooling of the non-metallic mineral slag floating on the surface of molten iron discharged in the process of blast furnace ironmaking, and then a kind of powder material obtained by grinding. The chemical composition of ground slag is similar to cement and its activity is higher. The grades are S75, S95 and S105. "S95" means that the activity index (also known as compressive strength ratio) of the ore powder reaches 95% at 28d. The more active the better, and of course the more expensive. The function of ore powder in concrete is mainly active effect.

(3) silicon powder: it is a very fine powder collected in the flue by dust collecting device in the ferroalloy factory when smelting ferrosilicon alloy or silicon metal. The chemical composition of silicon powder is mainly SiO2 (silicon dioxide), its particles are mainly amorphous spherical particles, smooth surface, very small particle size, small bulk density, very high activity, the price is also very expensive, generally used in high grade concrete ABOVE C80.

(4) Zeolite powder: is made of natural zeolite after mechanical grinding. Generally for porous multi-angle particles, water demand is larger, after adding zeolite powder concrete is more viscous. Local resource materials are used less.

3, aggregate
Aggregate is divided into coarse aggregate is also called stone, fine aggregate is also called sand. Sand is divided into natural sand, artificial sand, natural sand is divided into river sand, sea sand, mountain sand, artificial sand is divided into mechanism sand, mixed sand; According to the thickness of sand is divided into fine sand, medium sand, coarse sand. Stones are divided into crushed stones and pebbles; According to the continuity of particle size, it is divided into single particle size and continuous particle size. According to particle size, it is divided into 5-16, 5-20, 5-25, 5-31.5 (also known as 1-3 stone), 5-40 and so on.

(1) Gradation: refers to the distribution of each particle size in the aggregate. Generally speaking, poor gradation means that the aggregate particle size distribution is narrow, and there are more aggregates with single particle size. This aggregate has a great impact on concrete, such as: poor workability, poor pumping, stone, low strength, water consumption.

②, particle shape and surface state: particle shape can be divided into spherical or egg shape, angular shape, sheet shape and needle shape. Particle shape has a great influence on the bulk density. Generally speaking, the closer the particle is to the sphere, the higher the bulk density, and the more spherical particles, the higher the bulk density. The greater the accumulation density, the smaller the aggregate void rate, the more dense concrete, the higher the strength, the more concrete cement can be reduced. Surface state refers to the coarse dryness degree and pore characteristics of aggregate particle surface. Generally speaking, the surface of coarse dry aggregate and hardened cement stone has a good mechanical bite force, but the friction resistance is large, affecting the fluidity of concrete.

(3) Mud content: refers to the content of dust, silt and clay with particle size less than 0.075mm in the aggregate. The greater the mud content, the greater the water consumption of concrete, the lower the strength, the greater the dry shrinkage, the poor impermeability and the poor freeze-thaw resistance. National standard requirements: used for mixing C60~C30 concrete sand, mud content must be less than 3%, stone mud content must be less than 1%.

4. Admixture
Admixture is a kind of material added before concrete mixing or mixing process to improve the performance of new mixed concrete and hardened concrete. Admixture is an important component of modern concrete. It can be said that the technical progress of modern concrete is almost closely related to the application of admixture. The appearance of high efficiency water reducing agent promotes the development of high strength concrete, and also makes concrete pumping and self-compacting. The application of air entrainment agent greatly improves the antifreeze durability of concrete. Expansion agent plays an important role in cracking prevention of concrete structure. The use of antifreeze has made winter construction possible in the north, greatly extending the construction period. The kinds of admixture, performance is different, according to its main use function classification is divided into four categories: ① improve concrete mixing logistics performance admixture: water reducing agent (slump the same case to reduce the amount of water mixing), pumping agent (both reduce water, slow coagulation, air); (2) adjust the setting time, hardening performance admixture: retarding agent (prolong the concrete setting time admixture), coagulant (shorten the setting time), accelerating agent (make concrete rapid condensation such as jet concrete); (3) Improve concrete durability admixture: air entraining agent (introduce a large number of tiny bubbles, improve freezing resistance), waterproof agent (improve concrete water permeability resistance performance), rust inhibitor, and mineral additives; (4) improve the other performance of concrete admixtures: expansion agent (make concrete expansion), antifreeze (reduce the freezing point of water, in negative temperature to promote the strength of concrete growth, improve concrete freeze-thaw resistance performance), colorant (preparation of color concrete admixtures).

5, water
Concrete generally use tap water or clean groundwater, some industrial wastewater and sewage containing fat, oil, sugar, acid, salt can not be used to mix concrete, containing impurities, mud and other unclean water can not be used to mix concrete.