Fine-grained concrete, also known as sand concrete, is defined as the concrete in which the coarse aggregate is replaced by sand or any filler material. The maximum size of fine aggregates used in fine-grained concrete is 10 mm.
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Fine-grained concrete is gaining popularity in modern construction due to the following features:
- Fine-aggregates are highly manufacturable
- Can be used to construct a variety of structures
- Can be manufactured using inexpensive local sand or secondary sand
This article explores the significance and features of fine-grained concrete in comparison with conventional concrete.
Significance of Fine-Grained Concrete
Coarse aggregate is an essential ingredient in ordinary concrete mixture. In regions where there is a scarcity of coarse aggregates, fine-grained concrete can be used as an alternative. In fine-grained concrete, fine aggregate is used as the potential substitute for coarse aggregate.
Fine-grained concrete with various functional properties is obtained by altering the compositions and the structure of normal concrete using filler materials and additives. Fine-grained porous concrete with various densities and strength can be derived by using certain additives and technologies.
The area of application of fine-grained concrete is practically irreplaceable by any other type of concrete. Fine-grained concrete is used in the construction of:
- Thin-walled structures generally reinforced with polymer or steel woven nets
- Architectural forms
- Road coverings
Strength of Fine-Grained Concrete
An empirical formula was provided by Y. Bagenov to explain the dependence of fine-grained concrete strength (R) as:
A is the coefficient, whose value for high-quality materials A=0.8, for medium-quality A= 0.75 and for low-quality A= 0.65;
Va = Volume of entrained air;
C,W = Contents of cement and water in kg/m3;
Rc = Strength of cement, MPa.
Factors Affecting Strength of Fine-Grained Concrete
As fine-grained concrete is a concrete rich with sand and filler particles, the primary factor that governs its strength is the quality of fine aggregates. The quality of fine aggregates influences the basic properties of fine-grained concrete to a higher extent than for conventional concrete.
As per several studies, the replacement of coarse aggregate with fine sand in concrete reduces the strength by 25 to 30%. In some instances, it can decrease to two to three times the strength of conventional concrete.
In general, the factors affecting the strength of fine-grained concrete are:
- Cement-water ratio
- Strength of cement
- Quality of aggregates
- Placeability of fresh concrete
- Presence and quantity of admixtures
- Curing conditions
Figure-1 below shows the flow diameter (FD) and placeability (P) parameter for fine-grained concrete designed for different water-cement ratios (W/C).
Figure-2 below shows the variation of flexural strength (Rf) of fine-grained concrete with the ordinary concrete (Rcmp). The curves 1 and 2 represent the flexural strength of sand and ordinary concrete, respectively. The tensile strength of sand concrete is represented as 3.
The structural variations in fine-grained concrete affect their deformation properties. The fine-grained concrete has a modulus of elasticity 20 to 30% lesser than ordinary concrete. They also have a higher creep and shrinkage compared to ordinary concrete.
High-Performance Fine-Grained Concrete (HPFGC)
High-performance fine-grained concrete (HPFGC) is considered a new generation of sand concrete that can show strength, durability, and performance compared to high-performance concrete. The main composition of HPFGC is cement, sand, filler, admixture, and water. Here, a highly reactive pozzolan material is used to improve the properties from normal fine-grained concrete to HPFGC.
Effect of Additives on the Properties of Fine-Grained Concrete
Concrete is combined with multi-component systems instead of traditional materials to meet the market economy and bring solutions to construction problems. Composite binders like gypsum, magnesia binders, complex modifiers, mineral raw materials, and other intensive technologies can be used to convert normal concrete to multi-component composite concrete.
The application of fine-grained concrete in major civil and building construction is limited due to reduced shrinkage and crack resistance. The effect of shrinkage on the structural properties of fine-grained concrete is solved by introducing composite binders during their preparation.
The composite binders improve the manufacturability of construction and reduce the complexity during concrete pouring. The introduction of additives helps fine-grained concrete to take complex architectural forms.
Advantages of Fine-Grained Concrete
Fine-grained multi-component concrete has the following advantages:
- A finely divided homogeneous structure with high quality is obtained.
- The material modification of fine aggregate concrete using multi-components increases the efficiency of the concrete.
- Fine-grained multi-component concrete possesses high thixotropy and adaptability.
- Fine-grained concrete provides new architectural and structural solutions like hybrid structures, thin-walled structures, layered structures, products of variable density, pavements, etc.
- Fine-grained multi-component concrete can be developed to improve heat insulation, waterproofing, and decorative properties.
- Fine-grained concrete opens up the possibility to use local and low-cost materials over conventional coarse-grained concrete.
Fine-grained concrete is defined as the concrete in which the coarse aggregate is replaced by sand or any filler material. The maximum size of fine aggregates used in fine-grained concrete is 10mm.
Fine-grained concrete is used for the following applications:
1. Construction of hybrid structures
2. Construction of thin-walled structures
3. Construction of layered structures
4. Architectural decorations
5. Porous concrete pavement
6. Pavement coverings
The main factors affecting properties of fine-grained concrete are:
1. Cement-water ratio
2. Strength of cement
3. Quality of aggregates
4. Placeability of fresh concrete
5. Presence and quantity of admixtures
6. Curing conditions