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What is the impact of applying limestone powder to concrete?2023-08-31 13:33:11
With the rapid development of urban construction, there has been a continuous increase in the demand for concrete in engineering projects. Consequently, fly ash and slag concrete have gained significant popularity within the field of engineering construction. In China, due to geographical factors, there is an uneven distribution of slag and fly ash resources which results in shortages being observed in certain regions. On the other hand (Conversely), limestone resources are widely distributed throughout our country and possess strong economic viability; therefore they are extensively utilized (hence their extensive utilization). The addition of limestone powder as a filler to concrete proves immensely beneficial for enhancing its performance.
About Limestone
The properties of limestone include excellent processability, polishing capabilities, and strong cementation properties. It is insoluble in water but easily soluble in saturated sulfuric acid. Limestone can react with a strong acid to form the corresponding calcium salt while releasing CO2. When heated to temperatures above 900°C (generally 1000~1300°C), limestone decomposes into lime (CaO) and releases CO2. Upon contact with water, quicklime immediately forms hydrated lime [Ca(OH)2], which can be adjusted after dissolution in water and readily hardens in air. However, the primary application of limestone lies in its use for cement production where the white stone containing over 90% CaCO3 is crushed, graded, and separated using Raymond mill or other grinding mills.
The Impact of Limestone Powder on Concrete
Influence of limestone powder on working performance of concrete
1.1 Effect of limestone powder addition method on concrete performance
The addition of limestone powder has been observed to not only enhance the cement slurry content and improve fluidity but also reduce the mutual friction of sand through the lubricating effect of limestone powder, thereby enhancing concrete workability. Based on analysis and research findings, when limestone powder is incorporated into self-compacting concrete, it exhibits superior cohesiveness and fluidity compared to fly ash-based concrete with an equivalent water-to-ash ratio. In conclusion, the primary impact of limestone powder on concrete's performance lies in its ability to enhance fluidity. Furthermore, it mainly mitigates bleeding and segregation phenomena in comparison to low-strength concrete. Consequently, incorporating limestone powder as a mineral admixture in concrete represents a significant avenue for future research.
1.2 Effect of fineness of limestone powder on concrete properties
The fineness of limestone powder significantly affects the performance of concrete. When the activity of limestone powder is weaker than that of cement clinker, incorporating it as a partial replacement for cement reduces the involvement of cement clinker in initial hydration, leading to an increase in water-binder ratio and slump of concrete. Filling with finer limestone powder yields better results, resulting in relatively higher free water content in the concrete system.
Influence of Limestone on Durability of Concrete
2.1 Effect of limestone powder on dry shrinkage performance of concrete
The incorporation of limestone powder and rice husk ash not only effectively enhances the water retention capacity of mortar but also serves as an internal maintenance agent. Adding an appropriate amount of stone powder can exert its "micro-aggregate filling effect" and improve the internal structure. In the case of ordinary concrete, incorporating stone powder significantly reduces dry shrinkage compared to pure cement concrete with similar strength. For high-strength concrete, autogenous shrinkage gradually decreases when mixed with limestone powder, and a larger incorporation amount further reduces autogenous shrinkage.
2.2 Effect of stone powder on carbonization resistance of concrete
The influence of limestone powder on the carbonization resistance of concrete is related to the curing age, curing conditions, and the amount of limestone powder added. As the amount of limestone powder added increases, the carbonization resistance decreases. With an increase in standard curing age, the carbonization depth decreases. Compared to indoor standard curing, outdoor spraying water curing significantly improves the carbonization resistance of concrete. Additionally, as the specific surface area of limestone powder gradually increases, its carbonization resistance also increases. When mixed with stone powder and steel slag into single steel slag, the anti-carbonation ability of concrete will be reduced to varying degrees; however, this adverse effect is relatively small.
Limestone is Used For Concrete
The influence mechanism of limestone powder on the performance of concrete generally encompasses the following aspects.
(1)Morphology effect
The effect of particle morphology can be divided into two aspects: the morphology effect and the filling effect. On one hand, the smooth surface of limestone powder particles distributed among cement particles enhances their dispersion, thereby increasing particle spacing and improving concrete fluidity. Fine limestone powder particles also aid in deflocculating the flocculated structure formed by cement hydration. Additionally, partial replacement of cement with stone powder reduces its quantity and slows down the reaction speed of the entire system, resulting in improved workability and reduced slump loss of concrete. On the other hand, due to its small particle size, limestone powder forms a well-graded mixture with cement clinker and other mineral admixtures, providing excellent filling properties. Moreover, it fills in interstices between the cement slurry matrix and interfacial transition zone, leading to denser cement-interfacial structures with reduced porosity and pore diameter. This improves pore structure and ultimately increases both cement strength and interfacial strength.
(2)Activity effect
The activity of limestone powder is primarily demonstrated in two aspects: firstly, the reaction between CaCO3 in limestone powder and the aluminum phase of cement clinker; secondly, the generation of Ca(OH)2 through the hydration reaction of CaCO3 in limestone powder with cement. As the hydration reaction progresses, limestone powder and tricalcium aluminate react to form a carbonaluminate complex with certain gelation ability. This hydration product bonds with other hydration products to enhance the compactness of concrete, thereby improving its strength and durability.
(3)Accelerate hydration effect
When the limestone powder content is appropriate, the fine particles of limestone powder serve as a nucleation matrix for C-S-H, reducing the nucleation barrier and accelerating the hydration reaction rate while improving the distribution of cement hydration products. The addition of limestone powder accelerates hydration regardless of cement type, with greater fineness resulting in more pronounced early compressive strength growth.
Limestone Grinding Mill
YGM Raymond Mill
Capacity: 1-50 t/hFeed Size: 35 mm
Powder Fineness: 80-325 mesh
Compared to conventional mills, this equipment incorporates several patented technologies, resulting in significantly improved performance indicators. As a result, there has been an increase in production of over 40% and a reduction of more than 30% in the cost per unit of power consumption. The powder quality is excellent with exceptional particle shape and high powder yield. Additionally, it promotes energy saving and consumption reduction, making it the preferred exclusive equipment for numerous non-metallic mining projects. Raymond mill is a highly efficient alternative to ball mills for ore powder processing. The product offers outstanding advantages such as a robust system, high screening rate, stable transmission, high wear resistance, and easy maintenance. It finds extensive application in mining, building materials metallurgy chemical industries and other fields requiring grinding processing of mineral products. Raymond mill is widely used for milling processes involving materials like barite calcite potassium feldspar talc marble limestone ceramics glass with Mohs hardness not exceeding 7 and humidity below 6%, while being non-flammable or explosive.
HGM Ultrafine Grinding Mill
Capacity: 1-45 t/hFeed Size: ≤20 mm
Powder Fineness: 325-3000 mesh
The ultrafine mill is comprised of the main machine, analytical machine (powder separator), pipeline device, blower, finished cyclone separator, jaw crusher, hoist, electromagnetic vibration feeder, electric control motor and other components. The main machine of the calcium carbonate mill consists of a frame, air inlet volute, shovel knife, grinding roller, grinding ring cover shell and motor. During operation of the main machine in the calcium carbonate mill,the mill roller tightly rolls on the grinding ring under centrifugal force. The material is then conveyed to the middle of the mill roller and grinding ring by means of a shovel knife. Under the action of grinding pressure,the material is crushed into powder which is subsequently blown up by a fan and passes through an analysis machine. Material meeting fineness requirements goes through this analysis machine while material failing to meet requirements returns for further grinding in the chamber. Finally,the material is separated and collected through an analyzer's cyclone separator. Exhaust air with industrial filter cloth isolates exhaust air into powder.
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