Types, Properties and Uses in Concrete
Cementitious materials are fine mineral powders used as binding materials in concrete. When mixed with water, these materials undergo chemical reactions that form a strong, rigid mass which binds aggregate particles together. The most common cementitious material is Portland cement, although cement extenders such as fly ash, ground granulated blast-furnace slag (GGBS) and silica fume are also widely used.
This guide explains the different types of cementitious materials, the standards that apply in South Africa, their properties, and how they are selected for various concrete applications.
What Is Masonry Cement?
Masonry cement is a cement product designed primarily for bricklaying, block laying, rendering and plastering. Unlike common cements used in concrete production, masonry cements are formulated to improve workability and ease of application for masonry construction.
Masonry cements that comply with SANS 50413 are not intended for use in structural concrete.
According to the national foreword of SANS 50413, masonry cement is commonly used for:
- Bricklaying
- Block laying
- Rendering
- Plastering
Users should ensure that masonry cement is only used for its intended purpose. When producing concrete, contractors should select common cements that comply with SANS 50197, which are specifically designed to meet concrete strength and durability requirements.
Masonry Cement vs Portland Cement
A common question is whether masonry cement can be used instead of Portland cement in concrete.
The answer is generally no.
Portland cement forms the basis of common cements used in concrete and is designed to provide the strength and performance required for structural applications. Masonry cement is engineered primarily for workability in mortars and plasters and should not be substituted for concrete cement unless specifically approved by the project engineer or specification.
Cement Standards in South Africa
Cementitious materials used in concrete in South Africa must comply national standards that regulate composition, performance and quality.
Common cements used in concrete are governed by SANS 50197, while masonry cements are covered by SANS 50413. In addition, all cement sold in South Africa must comply with the requirements of the National Regulator for Compulsory Specifications (NRCS) under VC9085.
A compliant cement bag should clearly display:
- The cement strength class
- The cement composition designation
- A valid Letter of Authority (LOA) number issued by the NRCS
Each cement type and manufacturing source is issued its own LOA number, providing traceability and regulatory compliance.
The two primary cement standards are:
| Standard | Description |
|---|---|
| SANS 50197 | Applies to common cements used in concrete production. |
| SANS 50413 | Applies to masonry cements used for bricklaying, rendering and plastering. |
SANS 50197: Common Cement
SANS 50197 is the primary standard governing common cements used in concrete production.
It consists of two parts:
| Standard | Description |
|---|---|
| SANS 50197-1 | Composition, specifications and conformity criteria for common cements. |
| SANS 50197-2 | Conformity evaluation and compliance verification. |
Cement Composition Requirements
SANS 50197-1 classifies cement according to the proportion of its main constituents and any minor additional constituents.
The standard permits a wide range of cement compositions, including combinations of Portland cement clinker, blast-furnace slag, fly ash, silica fume, pozzolans and limestone fillers. However, not every combination allowed by the standard is commercially produced in South Africa.
The performance characteristics of a specific cement will depend on its composition and should be verified with the manufacturer where required.
Compressive Strength Requirements
SANS 50197-1 also defines cement strength classes and minimum performance requirements.
Strength testing is carried out in accordance with SANS 50196-1, which specifies standardised methods for determining cement strength using a water-to-cement ratio of 0.5.
It is important to note that this test method differs from the concrete cube strength tests commonly used on construction projects.
Cements must achieve specified early-age strengths after 2 or 7 days, depending on the strength class, as well as minimum 28-day strength requirements.
Other Compliance Requirements
In addition to composition and strength requirements, SANS 50197-1 includes a range of physical and chemical performance criteria.
Compliance is monitored through manufacturer quality-control procedures and verified through independent conformity assessment and audit testing in accordance with SANS 50197-2.
Compressive strength requirements of SANS 50197-1
| Strength Class | Compressive Strength, MPa | Initial Setting Time | |||
|---|---|---|---|---|---|
| Early Strength | Standard Strength | ||||
| 2 Days | 7 Days | 28 Days | min | ||
| 32,5La | - | ≥12,0 | ≥32,5 | ≤52,5 | ≥75 |
| 32,5N | - | ≥16,0 | |||
| 32,5R | ≥10,0 | - | |||
| 42,5La | - | ≥16,0 | ≥42,5 | ≤62,5 | ≥60 |
| 42,5N | ≥10,0 | - | |||
| 42,5R | ≥20,0 | - | |||
| 52,5La | ≥10,0 | - | ≥52,5 | - | ≥45 |
| 52,5N | ≥20,0 | - | |||
| 52,5R | ≥30,0 | - | |||
Permitted products in SANS 50197-1 and SANS 50197-5 (combined)
| Main types |
Notation of the products (types of cement) |
Composition (percentage by mass)a | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Main constituents | Minor additional constituents |
||||||||||||
| Clinker | Blast- furnace slag |
Silica fumeb | Pozzolana | Fly ash | Burnt shale |
Limestone | |||||||
| Natural | Natural calcined |
Siliceous | Calcareous | ||||||||||
| Type name | Type notation | K | S | D | P | Q | V | W | T | L | LL | ||
| CEM I | Portland cement | CEM I | 95–100 | - | - | - | - | - | - | - | - | - | 0–5 |
| CEM II | Portland-slag cement |
CEM II A-S | 80–94 | 6–20 | - | - | - | - | - | - | - | - | 0–5 |
| CEM II B-S | 65–79 | 21–35 | - | - | - | - | - | - | - | - | 0–5 | ||
| Portland-silica fume cement |
CEM II A-D | 90–94 | - | 6–10 | - | - | - | - | - | - | - | 0–5 | |
| Portland-pozzolana cement |
CEM II A-P | 80–94 | - | - | 6–20 | - | - | - | - | - | - | 0–5 | |
| CEM II B-P | 65–79 | - | - | 21–35 | - | - | - | - | - | - | 0–5 | ||
| CEM II A-Q | 80–94 | - | - | - | 6–20 | - | - | - | - | - | 0–5 | ||
| CEM II B-Q | 65–79 | - | - | - | 21–35 | - | - | - | - | - | 0–5 | ||
| Portland-fly ash cement |
CEM II A-V | 80–94 | - | - | - | - | 6–20 | - | - | - | - | 0–5 | |
| CEM II B-V | 65–79 | - | - | - | - | 21–35 | - | - | - | - | 0–5 | ||
| CEM II A-W | 80–94 | - | - | - | - | - | 6–20 | - | - | - | 0–5 | ||
| CEM II B-W | 65–79 | - | - | - | - | - | 21–35 | - | - | - | 0–5 | ||
| Portland-burnt shale cement |
CEM II A-T | 80–94 | - | - | - | - | - | - | 6–20 | - | - | 0–5 | |
| CEM II B-T | 65–79 | - | - | - | - | - | - | 21–35 | - | - | 0–5 | ||
| Portland-limestone cement |
CEM II A-L | 80–94 | - | - | - | - | - | - | - | 6–20 | - | 0–5 | |
| CEM II B-L | 65–79 | - | - | - | - | - | - | - | 21–35 | - | 0–5 | ||
| CEM II A-LL | 80–94 | - | - | - | - | - | - | - | - | 6–20 | 0–5 | ||
| CEM II B-LL | 65–79 | - | - | - | - | - | - | - | - | 21–35 | 0–5 | ||
| Portland-composite cementc d |
CEM II A-M | 80–88 | ← 12–20 → | 0–5 | |||||||||
| CEM II B-M | 65–79 | ← 21–35 → | 0–5 | ||||||||||
| CEM II C-M | 50–64 | ← 36–50 → | 0–5 | ||||||||||
| CEM III | Blast furnace cement |
CEM III A | 35–64 | 36–65 | - | - | - | - | - | - | - | - | 0–5 |
| CEM III B | 20–34 | 66–80 | - | - | - | - | - | - | - | - | 0–5 | ||
| CEM III C | 5–19 | 81–95 | - | - | - | - | - | - | - | - | 0–5 | ||
| CEM IV | Pozzolanic cementc |
CEM IV A | 65–89 | - | ← 11–35 → | - | - | - | 0–5 | ||||
| CEM IV B | 45–64 | - | ← 36–55 → | - | - | - | 0–5 | ||||||
| CEM V | Composite cementc |
CEM V A | 40–64 | 18–30 | - | ← 18–30 → | - | - | - | 0–5 | |||
| CEM V B | 20–38 | 31–50 | - | ← 31–49 → | - | - | - | 0–5 | |||||
| CEM VI | Composite cementc d |
CEM VI (S-P) | 35–49 | 31–59 | - | 6–20 | - | - | - | - | - | - | 0–5 |
| CEM VI (S-V) | 35–49 | 31–59 | - | - | - | 6–20 | - | - | - | - | 0–5 | ||
| CEM VI (S-L) | 35–49 | 31–59 | - | - | - | - | - | - | 6–20 | - | 0–5 | ||
| CEM VI (S-LL) | 35–49 | 31–59 | - | - | - | - | - | - | - | 6–20 | 0–5 | ||
Manufacture and Properties of Cementitious Materials
This section focuses on the cementitious materials most commonly available and used in South Africa, including portland cement and cement extenders.
Portland Cement
Portland cement forms the foundation of most concrete and cementitious systems used in construction. It is the primary ingredient in common cements manufactured in accordance with SANS 50197-1 and is also used in site-blended mixes that contain cement extenders.
The main raw materials used to manufacture portland cement are limestone and shale. These materials are carefully blended and heated in a kiln at extremely high temperatures to produce cement clinker. Once cooled, a small amount of gypsum is added before the clinker is ground into a fine powder known as portland cement.
How Portland Cement Works
When water is added to portland cement, a chemical reaction called hydration begins. During hydration, the cement paste gradually changes from a workable plastic state into a hard, durable solid that binds aggregates together to form concrete.
Hydration is an exothermic reaction, meaning it releases heat as the cement cures.
Two important compounds are produced during hydration:
- Calcium Silicate Hydrate (CSH) – the primary compound responsible for concrete strength and durability.
- Calcium Hydroxide (Lime) – helps maintain the highly alkaline environment within concrete, protecting reinforcing steel from corrosion.
Why Calcium Silicate Hydrate (CSH) Matters
Calcium silicate hydrate (CSH) is the most important hydration product in concrete. It provides much of the strength, density and impermeability that make concrete durable over time.
The greater the development of CSH within the concrete matrix, the stronger and more durable the hardened concrete becomes.
Portland Cement Extenders and Fillers
Portland cement extenders and fillers are materials used alongside portland cement and should not be used as standalone cementing products.
Common cement extenders used in South Africa include:
- Ground granulated blast-furnace slag (GGBS)
- Fly ash
- Limestone
These materials are often referred to as supplementary cementitious materials (SCMs) because they enhance the performance of concrete when combined with portland cement.
Benefits of Cement Extenders
The widespread use of cement extenders is driven by both economic and technical advantages:
- Lower material costs compared to pure portland cement
- Improved concrete durability
- Reduced permeability
- Better long-term performance
- Enhanced workability in some applications
- Reduced heat generation during hydration
The Fine-Filler Effect
Many cement extenders contain extremely fine particles that act as nucleation sites for the formation of calcium silicate hydrate (CSH).
This “fine-filler effect” helps create a denser concrete microstructure by reducing voids within the hardened cement paste and improving the bond between cement paste and aggregate particles.
As a result, properly designed concrete mixes containing cement extenders can achieve:
- Higher durability
- Improved impermeability
- Better resistance to aggressive environments
- Enhanced long-term strength development
The performance benefits of cement extenders generally increase as the replacement level increases, although the exact effect depends on the type of extender used and the concrete mix design.
Important: The benefits of cement extenders can only be fully realised when concrete is properly placed, compacted and cured.
Types of Cement Extenders Used in Concrete
Several types of cement extenders are used in modern concrete to improve strength, durability and long-term performance. These materials are commonly referred to as supplementary cementitious materials (SCMs) and are used together with portland cement.
Ground Granulated Blast-Furnace Slag (GGBS)
Ground granulated blast-furnace slag (GGBS) is a by-product of the iron-making process. Molten slag is rapidly cooled, or quenched, before being dried and ground into a fine powder.
When used in concrete, GGBS reacts with water and the alkaline environment created by portland cement to form additional calcium silicate hydrate (CSH), the primary compound responsible for concrete strength.
Because GGBS hydrates more slowly than portland cement, it generally produces lower early-age strength but can improve long-term durability and reduce permeability.
Benefits of GGBS in Concrete
- Improves long-term strength development
- Reduces permeability
- Improves durability
- Enhances resistance to aggressive environments
- Reduces heat generated during hydration
The performance of GGBS concrete depends on the type of cement used, the percentage of GGBS added and the fineness of the slag.
Fly Ash
Fly ash (FA) is collected from the exhaust gases produced during the combustion of finely ground coal. The finest particles are used as a cement extender in concrete.
Fly ash reacts with calcium hydroxide released during cement hydration to form additional calcium silicate hydrate (CSH). This reaction is known as a pozzolanic reaction, making fly ash an industrial pozzolan.
Because calcium hydroxide contributes little to concrete strength, converting it into additional CSH helps improve the efficiency of the cementing system.
Benefits of Fly Ash in Concrete
- Improves long-term strength
- Enhances workability
- Reduces permeability
- Improves durability
- Helps produce denser concrete
Fly ash is one of the most widely used supplementary cementitious materials in concrete worldwide.
Silica Fume
Silica fume (SF) is an ultra-fine powder produced as a by-product of ferro-silicon manufacturing.
Like fly ash, silica fume reacts with calcium hydroxide through a pozzolanic reaction to produce additional calcium silicate hydrate (CSH). However, silica fume particles are significantly smaller than cement particles, allowing them to fill microscopic voids within the concrete matrix.
This combination of chemical and physical effects results in stronger, denser and less permeable concrete.
Benefits of Silica Fume in Concrete
- Significantly increases strength
- Reduces permeability
- Produces a denser microstructure
- Improves durability
- Enhances resistance to water and chemical penetration
Due to its extremely fine particle size, silica fume is often used together with plasticising admixtures to improve dispersion and workability.
Limestone Filler
Limestone filler is finely ground limestone that has not undergone chemical processing.
Unlike fly ash, silica fume and GGBS, limestone filler is largely inert when mixed with cement and water. Its primary role is as a fine filler that improves particle packing and workability.
Limestone filler may be used in common cements and masonry cements, depending on the product formulation.
Under SANS 50197-1, limestone fillers are classified as:
- L – Total organic content not exceeding 0.50% by mass
- LL – Total organic content not exceeding 0.20% by mass
Limestone Filler vs Lime
Limestone filler used in cement should not be confused with:
- Building lime (hydrated lime)
- Road lime
- Quick lime
- Agricultural lime
Although these materials are chemically related, they serve different purposes and have different performance characteristics.
Cements complying with SANS 50197-1 do not contain quick lime (CaO) or hydrated lime (Ca(OH)₂) as cementing ingredients.