Reactive Powder Concrete (RPC)
What is reactive powder concrete (RPC)
Reactive powder concrete (RPC), as a type of ultra-high-performance concrete (UHPC), is a cement-based composite material with high compressive strength, high durability, high toughness, low porosity. The name RPC is given due to the improved fineness and reactivity of the components.
Reactive powder concrete is composed of cement, well-graded sand (with an average particle size between 0.1μm and 1mm, no coarse aggregate), quartz powder, silica fume, superplasticizer and steel fibers. It can be produced by appropriate treatments, such as pressure and heat treatments, in setting and hardening processes. The formulation principle is based on the theory of maximum density, that is, by improving the fineness and reactivity of the components, the internal defects (pores and microcracks) of the material are reduced to a minimum, so as to obtain good durability and the maximum bearing capacity determined by the component materials. Its excellent mechanical and physical properties are incomparable to normal concrete (NC) and conventional high-performance concrete (HPC).
The compressive strength of RPC can reach 200-800MPa. RPC can be divided into two classes according to the level of compressive strength, RPC200 (class 200 MPa) and RPC800 (class 800 MPa). Although the strength of RPC200 is much lower than that of RPC800, because RPC800 requires special setting and curing conditions, RPC200 are more often to be used currently. And RPC200 has a flexural strength of 30 to 60 MPa, which effectively overcomes the high brittleness of conventional high-performance concrete.
|Compressive strength (MPa)||170-230||500-800||60-100||20-50|
|Flexural strength (MPa)||30-60||45-140||6-10||2-5|
|Elastic modulus (GPa)||40-60||65-75||30-40||30-40|
|Fracture toughness (kJ/m2)||20-40||1.2-2||0.14||0.12|
In addition, RPC200 also has good ductility, and its fracture toughness is comparable to that of steel. And because the internal porosity of RPC is very small, it has excellent durability, impermeability, resistance to chloride ion penetration, carbonization, abrasion, and freezing and thawing. Under the condition of the same bearing capacity, the cement consumption of RPC material is almost half of that of normal concrete and HPC, so the CO2 emissions during the production of the same amount of cement are only about half. In the production process, the amount of non-renewable natural resource aggregates of RPC only accounts for 1/3 and 1/4 of HPC and 30MPa concrete, respectively.
Basic design principle of RPC
To improve the fineness and reactivity of the material components, reduce the internal defects (pores and microcracks) of the material, and obtain ultra-high strength and high durability. The purpose of the average particle size of the raw materials used by RPC is to minimize the porosity in the concrete and improve the compactness of the mixture.
Preparation of RPC
The preparation of RPC takes the following measures: Remove coarse aggregate to improve the mechanical properties of cement, eliminate the interfacial transition zone between the aggregate and cement paste to improve the homogeneity of the matrix; Optimize the particle gradation, apply pressure treatment during the setting period to increase the bulk density, and improve the compactness of the mixture. After setting, through heat treatment, the reactivity of RPC can be fully exerted and the microstructure can be improved; Steel fibers are added to improve toughness.
Composing material of RPC
- Cement: high silicic acid, low C3A content;
- Aggregate: well-graded sand, quartz powder;
- Superplasticizer: the dosage is 1.4%-1.8% (mass), which is 3 to 5 times the general dosage;
- Silica fume: the optimal filling amount is 25% of cement (mass);
- Steel fiber: for high strength, 3mm steel fibers with a dosage of 600kg/m3; for high toughness and low strength, 12.5mm steel fibers with a dosage of 191kg/m3.