In the asphalt mixture composition, mineral powder is the fine aggregate ground from limestone, basalt and other alkaline stones with particle size less than 0.075mm. It is an indispensable key component of asphalt mixture. Although the proportion of mineral powder is far less than that of coarse aggregate, it plays a decisive role in the internal structure, bonding performance, water stability and overall durability of asphalt mixture.Mineral powder is not a simple filler, but can be combined with asphalt to form high strength asphalt mortar, coating coarse and fine aggregate, which fundamentally determines the molding quality and service life of asphalt pavement.This paper systematically expounds the core function, action mechanism and construction control points of mineral powder in asphalt mixture.

Filling the voids of the skeleton and optimizing the dense structure of the mixture

Asphalt mixture is composed of coarse aggregate, fine aggregate, mineral powder and asphalt. A large number of microscopic voids will be formed after the coarse aggregate is embedded and extruded. If the voids are not effectively filled, the overall void ratio of the mixture is too large, which will lead to early diseases such as pavement seepage, loosening, spalling and cracking.The fine ore particle size is very small and the fineness is uniform, which can accurately fill the tiny gaps caused by the accumulation of coarse and fine aggregates and effectively reduce the internal pore volume of the mixture.
Through the filling effect of mineral powder, asphalt mixture changes from loose embedded structure to dense skeleton dense structure, greatly improves the overall compactness and reduces the permeability of pavement.The dense mixture structure can effectively prevent rainwater and groundwater from penetrating into the interior of the pavement, avoid the subgrade and base layer from being soaked and softened by water, reduce the aging corrosion of air and moisture to asphalt, and improve the overall stability and damage resistance of asphalt pavement from the structural level.

It forms asphalt mortar with asphalt to strengthen bonding and anchoring performance

This is the core and most critical engineering function of mineral powder.Pure asphalt itself has limited viscosity and low bond strength. When the aggregate is wrapped separately, it is easy to have problems of weak bonding and loose peeling.The high-quality mineral powder in the project is mostly processed from alkaline stone, with high surface activity and strong adsorption affinity with asphalt.
After mineral powder is mixed with mixture, it can absorb resin and asphaltene in asphalt evenly, and fully fuse with asphalt to form asphalt mortar with higher viscosity, stronger adhesion and better toughness.This glue will tightly wrap the surface of coarse and fine aggregates, forming a uniform, thick and stable adhesive oil film, which will firmly adhere the dispersed aggregate particles into a whole.Compared with pure asphalt, the adhesion and cohesion of asphalt mortar are greatly improved, which can effectively resist vehicle load rolling and road deformation pulling, avoid aggregate falling off and loose road surface, and significantly improve the overall integrity and mechanical strength of mixture.

Improve water stability and inhibit asphalt spalling

Water damage is the most common early disease of asphalt pavement. After rainwater infiltrates into the mixture, it is easy to replace the asphalt film on the surface of aggregate, resulting in asphalt and aggregate peeling, pavement pits, particle loss, net crack and other problems.The addition of mineral powder can fundamentally improve the water damage resistance and optimize the water stability of the mixture.
On the one hand, alkaline mineral powder can neutralize acidic substances in asphalt, optimize the interface bonding state between asphalt and aggregate, greatly improve the adhesion between asphalt film and aggregate surface, so that asphalt film is not easy to be peeled by moisture; on the other hand, mineral powder fills micro voids, blocks moisture penetration channels, and reduces moisture retention and diffusion in the mixture.At the same time, the dense asphalt mortar can wrap the micropores on the surface of the closed aggregate, block water and gas erosion, effectively prevent asphalt spalling and mixture loosening, and greatly prolong the service life of the pavement.

Adjust mixture gradation, optimize construction workability

The gradation continuity of asphalt mixture directly affects the paving and compaction effect of construction. The natural coarse and fine aggregate ratio often has the problems of gradation fault and insufficient fine material, which leads to poor workability of mixture, uneven paving and great compaction difficulty.As fine filler, mineral powder can perfectly fill up the grading short board and perfect the continuous grading system of mixture.
The reasonable amount of mineral powder can improve the uniformity and fluidity of the mixture, make the asphalt mortar fully lubricate the aggregate particles, reduce the friction resistance between the aggregates, make the mixture more uniform and non-segregation in the paving process, and make it easier to compact and form during the rolling construction, effectively improving the flatness and uniformity of the pavement.At the same time, mineral powder can fine-tune the key indicators such as porosity and saturation of the mixture, so that the performance of the mixture conforms to the specifications and standards, and adapts to different construction scenarios and process requirements.
Improve high temperature stability and resist permanent deformation of pavement
Under high temperature environment in summer, pure asphalt is easy to soften, viscosity decreases, overall stiffness of mixture decreases, and permanent deformation diseases such as rutting, wrapping and displacement are easy to occur under repeated rolling of vehicles.Mineral powder is hard in texture and stable in performance. It has no deformation and softening characteristics at high temperature. After mixing with asphalt mortar, the high temperature stiffness and deformation resistance of mortar can be greatly improved.
Mineral powder particles can form micro-skeleton support in the mortar, restrict the flow of asphalt at high temperature, improve the overall high temperature shear resistance and rolling resistance of the mixture, effectively inhibit diseases such as high temperature rutting and pavement displacement, ensure the flatness and structural stability of asphalt pavement in high temperature season, and greatly improve the heavy load resistance of the road.

Engineering control points of mineral powder content

The effect of mineral powder depends on reasonable dosage, not the higher dosage, the better effect.If the mineral powder content is too low, it is impossible to form sufficient high-quality asphalt mortar, the filling, bonding and waterproof effects are greatly weakened, and the mixture is easy to loose and seep; if the content is too high, it will lead to the increase of asphalt mortar hardness and brittleness, the low temperature crack resistance of the mixture will decrease, and the pavement will be easy to crack at low temperature, and at the same time, it will increase the difficulty of mixing the mixture.
The mineral powder content of conventional hot-mix asphalt mixture is generally controlled at 4%~7% of the total mass of mineral aggregate. During construction, it is necessary to accurately determine the mineral powder content according to aggregate grading, asphalt type and road conditions. Meanwhile, the mineral powder quality shall be strictly controlled to prevent moisture, agglomeration and excessive mud content from being put into use, so as to ensure that the mixture performance is stable and up to standard.

Summary

Mineral powder plays multiple core roles in asphalt mixture, such as filling, bonding, waterproof, shape stabilization and construction performance optimization. It is the key fine aggregate to construct dense and stable asphalt mixture structure and ensure pavement durability. Reasonable mineral powder content is one of the core links in asphalt mixture mix ratio design.At the same time, there is no universal fixed value for asphalt additive amount of asphalt mixture, and there is a clear empirical reference interval for all kinds of conventional mixtures, but the precise amount must be determined by Marshall test mix ratio design, combined with raw material characteristics, construction environment and road load grade dynamic optimization.The core logic of the project is as follows: fine aggregate, modified asphalt, low temperature construction and light load scenario shall be appropriately increased; coarse aggregate, matrix asphalt, high temperature construction and heavy load scenario shall be appropriately reduced. Finally, the optimal asphalt dosage shall be determined through test verification and field trial paving, and the long-term stable and durable operation of asphalt pavement shall be guaranteed in two ways in combination with reasonable mineral powder blending ratio.