Cements in Traditional Concrete Mixes

Cement Types in Concrete Mixes: ASTM C-150 and More

Cement plays a crucial role in the production of concrete, serving as the binding agent that holds aggregates together to create strong, durable structures. In traditional concrete mixes, the selection of cement can have a significant impact on the final product's performance, workability, durability and cost. When you are producing concrete with a volumetric mixer, the cementitious materials can be a broad category due to the versatility of the machine. For this post, we are going to focus on traditional cements in "regular" concrete mixes. 

With advancements in technology and increased focus on sustainability, we have seen a massive increase in the use of alternative cements. These cement types are gaining traction, including the growing use of Type IL cement as an alternative to traditional Type I/II. Let's explore the five primary cement types under ASTM C-150 and discuss the rise of Type IL, along with other alternatives such as Type 1P.

The Five Primary ASTM C-150 Cement Types

ASTM C-150, the standard specification for Portland cement, outlines five primary types of cement commonly used in traditional concrete mixes. Each type has unique properties that make it suitable for specific applications. Here's a breakdown:

Type I: General Purpose Cement

Type I cement is the most commonly used cement in general construction. It is designed for projects where special properties, such as high sulfate resistance or low heat of hydration, are not required. Think of it as the "standard" cement used in sidewalks, buildings, and pavements. It's versatile, cost-effective, and works well in most environments.

Type II: Moderate Sulfate Resistance

Type II cement is specifically designed to protect concrete against sulfate attack, which occurs when sulfates—naturally occurring salts found in soil, groundwater, and seawater—react with the hydrated compounds in cement. This reaction can cause expansion, cracking, and deterioration of the concrete over time. Sulfates are particularly problematic in areas with high soil salinity or in regions where concrete structures are exposed to sulfate-bearing water. The use of Type II cement helps mitigate this by incorporating chemical compositions that resist sulfate attack, making it ideal for foundations, piers, or any structures that come into contact with sulfate-rich environments. It also produces less heat during hydration, which reduces the risk of thermal cracking in large pours.

Type III: High Early Strength

When speed is of the essence, Type III cement comes into play. This cement is designed for situations where early strength development is critical, such as in fast-track construction projects or cold weather applications. Type III allows concrete to reach strength quickly, reducing the time needed before forms are stripped or construction can proceed.

Type IV: Low Heat of Hydration

Type IV cement is rarely used today but was designed for massive structures like dams, where controlling heat generation during hydration is essential. As the cement hydrates and hardens, it generates heat, leading to internal cracking if not properly managed. Type IV helps reduce this risk by producing less heat over time.

Type V: High Sulfate Resistance

For environments with high sulfate concentrations, Type V cement is similar to Type II and offers the highest level of sulfate resistance. It is commonly used in industrial applications, sewage treatment plants, and areas with harsh soil conditions. By resisting sulfate attack, Type V helps prolong the life of concrete in these aggressive environments.

Quite often a cement’s performance can overlap with multiple specifications. This is why you sometimes see a cement listed as a Type I/II or Type II/V. The type of cement that is available in your region will typically be what is required for the sulfate and soil conditions that are present.  

The Rise of Type IL Cement: A Sustainable Alternative

In recent years, there has been a growing trend towards using Type IL cement (Portland-limestone cement), especially as the industry focuses more on reducing carbon emissions. Type IL contains more finely ground limestone (up to 15%) than Type I/II cement.

Benefits of Type IL Cement:

• Lower Carbon Footprint: One of the main drivers behind the increased use of Type IL cement is its ability to reduce greenhouse gas emissions associated with cement production. By replacing a portion of the clinker with limestone, manufacturers can produce cement with a lower carbon footprint without sacrificing performance.
• Comparable Strength and Durability: Despite its lower clinker content, Type IL cement offers strength and durability comparable to that of Type I/II cement. In fact, in many cases, Type IL has been shown to perform similarly or better over time due to the enhanced particle packing of the fine limestone. The exact ratio for replacement is still open to some debate. Comparison of mill certifications and working with your cement supplier will point you in the right direction. If there is still some concern, we recommend comparative testing to indicate whether it is one-for-one.

Challenges with Type IL Cement:

• Adjustment to Mix Designs: Concrete producers and contractors must adjust their mix designs when switching from Type I/II to Type IL. The cement's slightly different properties may affect water demand, set times, and admixture compatibility, so careful testing is essential.
• Perception and Acceptance: Although Type IL is gaining popularity, there is still some hesitancy in the market due to unfamiliarity with the product. Engineers and contractors must be educated on its benefits to increase the widespread acceptance in traditional concrete applications.
• Mix Designs and Finishing: Most cement companies contend that a one-to-one exchange with Type I can be done, and all other facets remain the same. However, a number of producers and finishers are reporting differences. As a producer, you need to test your mixes when you switch. You may find increased water demand, variable / longer set times, cracking, and porous surfaces. Most of these issues can be addressed through adjusted mix designs, admixtures, and finishing procedures.
• Use with Fly Ash: Though anecdotal, the testing that we have seen and discussed with others shows that Type IL will need a lower replacement rate for fly ash usage to hit target strengths. In cases where a 75% cement to 25% fly ash ratio would work for Type I, testing will indicate if that ratio is more like a 80% cement to 20% fly ash ratio.  

Type 1P Cement: Another Alternative for Sustainability

 Another cement type gaining attention is Type 1P, or Portland-pozzolan cement. Similar to Type IL, Type 1P replaces a portion of the clinker with supplementary materials, in this case, pozzolans such as fly ash, silica fume, or natural pozzolanic materials.

 Benefits of Type 1P Cement:

• Enhanced Durability: The use of pozzolans in Type 1P cement can enhance the long-term durability of concrete, particularly in aggressive environments. Pozzolans improve resistance to chemical attacks, reduce permeability, and increase the lifespan of the concrete structure.
• Lower Environmental Impact: Like Type IL, Type 1P cement helps reduce carbon emissions by replacing a portion of clinker with pozzolanic materials, many of which are byproducts of other industrial processes.

  Challenges with Type 1P Cement:

• Extended Set Times: One challenge with Type 1P cement is that pozzolans can slow down the setting time of concrete. This can be mitigated through the use of accelerators, but it is a factor that must be considered in time-sensitive projects.
• Availability: Type IP mixes are not available in all markets. In fact, they have become harder to find as Pozzolans are in limited supply and more expensive to secure.

Common Issues in Concrete Mixes Associated with Cement

While cement is a key ingredient in concrete, it may also influence several issues or challenges that can arise if not properly managed:

• Heat of Hydration: As previously mentioned, cements like Type I and Type II can generate significant heat during hydration. In large pours, this can cause thermal cracking if not controlled. In some cases, like rapid setting concrete or cold weather, you may want the heat and therefore avoid low heat of hydration cements.
• Compatibility with Admixtures: Different cement types may react differently with admixtures, such as water reducers, accelerators, or air-entraining agents. This can be regional in nature as the raw materials will influence the performance. It is also directly related to volumetric mixers and the short mixing times. Testing is crucial to ensure optimal performance.
• Sulfate Attack: Using the wrong cement type in sulfate-rich environments can lead to deterioration over time. The sulfates will attack the cement matrix and cause significant damage. Always select the appropriate cement type based on the exposure conditions. Cement companies will most often offer the cement required in your area but checking the specifications for any job to confirm is always the right choice.
• Setting Times: Switching from traditional Type I/II cement to alternatives like Type IL or Type 1P can affect the setting time, requiring adjustments in scheduling, admixtures, placing and finishing.
• Alkali-Silica Reaction (ASR): ASR occurs when reactive silica in aggregates comes into contact with alkalis (sodium and potassium) in cement, forming a gel that expands when exposed to moisture. This expansion can lead to cracking and long-term durability issues in concrete. To mitigate ASR, it’s important to use low-alkali cements, supplementary cementitious materials (SCMs) like fly ash or slag, non-reactive aggregates or specialty admixtures.
• False Setting in Volumetric Mixers: False setting can be a particular challenge for volumetric mixer operations. This is a phenomenon where the cement stiffens prematurely after mixing but can regain workability with additional mixing. False setting is often caused by the dehydration of gypsum in the cement, typically due to poor storage conditions or manufacturing inconsistencies. In these cases, looking for an alternate cement source is the best option though use of SCM’s and some admixtures may help.

 Conclusion: Choosing the Right Cement for the Job

 Selecting the right cement type for your project is critical to ensuring the performance and longevity of your concrete. While Type I and Type II cements remain industry staples, the increased use of Type IL and alternatives like Type 1P offer more sustainable options for today's construction projects. Understanding the properties and challenges of each cement type will help you make informed decisions and optimize your mix designs.

 At Concrete Business Solutions, we specialize in helping businesses optimize their concrete production operations, whether you're using traditional cement types or exploring newer, more sustainable options. Visit our website, www.concretebs.com, for more information on our services and training for volumetric mixer operations and admixture use. Let's work together to build a stronger, more sustainable future.