KSC Type-K Cement — FAQs
Cement for KSC Type-K Shrinkage-Compensating Concrete
KSC CONCRETE TECHNICAL GUIDE [PDF]
1. What is KSC Type-K Cement?
2. What is the KSC Komponent® system?
3. What is KSC System-K™?
4. What are the specifications that are now in effect that can be used for guidelines?
5. What makes shrinkage-compensating concrete different from ordinary concrete?
6. Where can I use shrinkage-compensating concrete?
7. What can’t shrinkage-compensating concrete do?
Structural Design Questions
1. What is the recommended joint spacing?
2. What are the steel requirements?
3. What about KSC System-K™ and structural steel?
4. Where are KSC Type-K, KSC Komponent®, and KSC System-K™ available?
5. Can we guarantee a crack-free project?
6. How does shrinkage-compensating cement gain strength compared to Type I?
Mix Design Questions
1. Why the higher water/cement ratios?
2. Does air entrainment react differently with shrinkage-compensating concrete mix?
3. Why the higher cement content?
4. Why is there no bleed water?
5. Is KSC Type-K an admixture?
6. Is KSC Komponent® an admixture?
7. How is KSC Komponent® incorporated into the concrete mix?
8. I hear we have two yards less concrete in the truck.
Storage and Handling Questions
1. Where are CTS shrinkage-compenstating concrete products available?
2. Will shrinkage-compensating cement disrupt my operation?
3. What do I do with the leftover shrinkage-compensating cement?
4. KSC Type-K sticks to the fins of my drums on my concrete trucks.
1. Do we need special tools or knowledge?
2. Can we add water at the jobsite?
3. Will the shrinkage-compensating concrete blow up the forms with this expansion?
4. What about curing? Can we use a spray-on curing compound?
Q: What is KSC Type-K Cement?Structural Design Questions
A: According to ACI 223, KSC Type-K expansive cement is a shrinkage-compensating cement which, when mixed with water, forms a paste that, after setting, tends to increase in volume to a specifically greater degree than portland cement paste. It is used to compensate for volume decreased due to shrinkage or to induce tensile stresses in reinforcement. The expansion of KSC Type-K Cement when mixed with sufficient water is due primarily to the formation of the crystal ettringite. Concrete made with KSC Type-K Cement is known as shrinkage-compensating concrete.
Q: What is the KSC Komponent® system?
A: The KSC Komponent® system is a method for making KSC Type-K Cement at the batch plant by using approximately 15% expansive component from CTS Cement Manufacturing Corporation, and 85% of your local portland cement. This is usually a lower-cost method of making shrinkage-compensating concrete.
Q: What is KSC System-K™?
A: KSC System-K™ is a combination of KSC Komponent® and small synthetic fiber known as K-Fiber™. The K-Fiber™ replaces temperature steel (steel in place solely for crack control) in concrete, providing the necessary restraint. Recent price spikes in steel reinforcement have made KSC System-K™ a very economical choice for shrinkage-compensating concrete. The most common applications for KSC System-K™ are concrete slabs on grade, but it can be used in any concrete application where minimizing shrinkage cracking is desired.
Q: 4. What are the specifications now in effect that can be used for guidelines?
A: CTS Cement can provide you with recommended specifications for KSC Type-K, KSC Komponent®, and KSC System-K™ concrete. The following publications may also be helpful:
Q: What makes shrinkage-compensating concrete different from ordinary concrete?
- ASTM C806 (Test Method for Restrained Expansion of Expansive Cement Mortar).
- ASTM C845 (Standard Specification for Expansive Hydraulic Cement).
- ASTM C878 (Test Method for Restrained Expansion of Shrinkage-Compensating Concrete).
- ACI 223 (Standard Practice for Use of Shrinkage-Compensating Concrete).
- ACI SP-2 (ACI Manual for Concrete Practices) Page 374-381.
- Ohio Department of Transportation (Expansive Hydraulic Cement).
- Ohio Turnpike Commission — 5P5 1 1A (Class S Concrete, Using Shrinkage-Compensating Cement).
- U.S. Corps of Engineers — Standard Practice for Concrete (Emi 110-2-2000). 5.
A: When regular portland cement concrete hardens and begins to dry out, a negative volume change occurs in the total mass. This process is called drying shrinkage. Shrinkage of concrete sets up internal tensile stresses, and if these stresses exceed the tensile strength of the concrete, cracking, called drying shrinkage cracks occur. The shrinkage-compensating concrete expands slightly during the early stages following placement and when restrained by reinforcement, puts mass into compression. The mass returns to its original size, when the effects of drying shrinkage occur, relieving the compressive stresses related to regular portland cement. The result is a concrete that can minimize drying shrinkage cracks and offer advantages in design and construction over conventional portland cement concrete.
Q: Where can I use shrinkage-compensating concrete?
A: Shrinkage-compensating concrete can be used in any application that a regular portland cement concrete is used, including, but not limited to reinforced and post-tensioned structural slabs and slabs on grade, walls, topping, grouts, and pre-cast elements.
Q: What can’t shrinkage-compensating concrete do?
A: Shrinkage-compensating concrete cannot eliminate all types of cracking. There are many types of cracking such as settlement cracks, structural cracks, cracks caused by creep of concrete over long periods, and plastic shrinkage cracks while concrete is in the semi-plastic state.
Q: What is the recommended joint spacing?Mix Design Questions
A: What is acceptable and economical while maintaining the 3:1 length-to-width ratio? It is recommended that areas exposed to thermal movement be limited to 100 x 100 feet. We have in the past placed in excess of 30,000 square feet without any jointing.
Q: What are the steel requirements?
A: Minimum steel requirements are 0.15% of cross-sectional area, however, structural considerations must be observed. The steel should also be a cap of two inches from the top surface of the concrete.
Q: What about KSC System-K™ and structural steel?
A: The K-Fiber™ in KSC System-K™ cannot replace structural steel reinforcement. However, the structural steel will not hinder the effectiveness of KSC System-K™.
Q: Where are KSC Type-K, KSC Komponent®, and KSC System-K™ available?
A: Any place in North America that it is desired. It can be shipped in bags, by bulk, or by rail.
Q: Can we guarantee a crack-free project?
A: No, but shrinkage-compensating concrete will minimize shrinkage cracks and greatly reduce the need for shrinkage-control joints. If cracking does occur, it will be greatly reduced, and the cracks that do occur will be tighter.
Q: How does shrinkage-compensating cement gain strength compared to Type I?
A: Shrinkage-compensating cement has a slower strength gain from one to seven days than normal Type I cement. We do grind KSC Type-K finer to compensate for this. The seven to 28-day strength gain after ettringite crystals have grown is comparable to Type I. The water cement ratio is the greatest factor effecting shrinkage-compensating cement strength, as it is with Type I cement.
Q: Why the higher water/cement ratios?Storage and Handling Questions
A: Shrinkage-compensating cement needs about 10% to 15% more mixing water than standard cement to accommodate the formation of the ettringite. Water cement ratios are typically 0.45 to 0.50 for interior concrete and 0.50 to 0.55 for exterior. We like to see the concrete batched at a seven-inch slump at the concrete plant because of the high demand for water, which usually occurs initially when mixing water with shrinkage-compensating cement.
This high demand is caused by the:
We can look for a one-to-three inch slump loss within the first 30 minutes. Shrinkage-compensating concrete should be placed at a five plus/minus one-inch slump.
- Hydration of the cement
- The ettringite growth starts immediately, and
- We are wetting materials.
Q: Does air entrainment react differently with shrinkage-compensating cement?
A: With very few exceptions, air entrainment admixtures that comply with ASTM C260 may be used for the same purpose with shrinkage-compensating concrete as with other types of portland cement concrete. Generally, the same amount of a given air-entraining admixture will produce a comparable percentage of entrained air, all other conditions being equal. (ACI 223-98 4.4.1). Please call your CTS Cement representative for guidance in selecting an air-entraining admixture for your shrinkage-compensating cement.
Q: Why the higher cement content?
A: A minimum of 470 lbs of portland cement and 90 lbs of Komponent® is recommended to develop sufficient tensile strength in the concrete and sufficient expansive force to reduce the potential for cracking. Lower cement content or lower dosages of KSC Komponent® will usually result in a higher cracking potential.
Q: Why is there no bleed water?
A: The formation of ettringite uses the extra mix water, thus eliminating the bleed water.
Q: Is KSC Type-K an admixture?
A: No. It is not an admixture. It is a true ASTM C845 cement.
Q: Is KSC Komponent® an admixture?
A: KSC Komponent® is not an admixture in the traditional sense, but one could think of it as a mineral admixture. Blending approximately 15% KSC Komponent® with 85% portland cement results in ASTM C845 KSC Type-K Cement. This is the basis of the KSC Komponent® system.
Q: How is KSC Komponent® incorporated into the concrete mix?
A: Generally, this is done at the batch plant. If you are not adding the KSC Komponent® via silo, the easiest way is to break the KSC Komponent® bags over the sand and stone on the aggregate belt prior to batching the concrete. After combining the water, cement, aggregate, and KSC Komponent®, the drum should be rotated about 70 times at mixing speed. This helps ensure complete incorporation of the KSC Komponent® into the mix.
Q: I hear we have two yards less concrete in the truck.
A: With good normal procedures, the same size loads can be hauled. However, most Departments of Transportation require two yards less on their projects.
Q: Where are KSC shrinkage-compensating concrete products available?Placement Questions
A: Everywhere. Contact your CTS Cement representative for details.
Q: Will shrinkage-compensating cement disrupt my operation?
A: We need to plan ahead. We can help out with planning to make the project go easier. We have ideas about dropping tankers with the cement in them, using fly-ash silos. There are a number of ways to work around these types of problems. What does it take? PLANNING AHEAD and notifying your CTS Cement representative.
Q: What do I do with the leftover shrinkage-compensating cement?
A: Shrinkage-compensating cement can be used in footers or in other non-spec work. Type I can be pumped right on top of it and blended if there is not much left over. Calcium chloride can be added to KSC Type-K, killing the ettringite and reverting the leftover KSC Type-K to Type I.
Q: KSC Type-K sticks to the fins of my drums on my concrete trucks.
A: Fin build-up is primarily due to insufficient mix water or lack of enough mixing revolutions. Use about 1,000 lbs. of stone and enough water to let the mix act like a scouring pad in the truck. The stone can be reused.
Q: Do we need special tools or knowledge?
A: Standard finishing tools and equipment are used. Any distinctive characteristics can be covered during the pre-construction and pre-placement meetings. It is also suggested that a representative from CTS be contacted prior to the initial pour for consultation.
Q: Can we add water at the jobsite?
A: This is up to the test lab or the engineer. The rule of thumb is two gallons of water per one-inch slump per yard of concrete. If the batch ticket shows less water than the designed water/cement ratio, that much water up to the design may be used.
Q: Will the shrinkage-compensating concrete blow up the forms with this expansion?
A: No, the shrinkage-compensating concrete does not expand that quickly or that much. We are talking about very small expansions in terms of lengths, and a good rule-of-thumb to remember is that the cement expands and the reinforcement resists the expansion of the concrete.
Q: What about curing? Can we use a spray-on curing compound?
A: Proper curing is very important to ensure a successful shrinkage-compensating concrete project. Curing compounds Do NOT provide sufficient curing for the concrete. The rule is the surface of the concrete must remain continuously wet for a full seven days. There are many ways to accomplish this. The simplest is to dam the sides of the concrete and flood the surface. Alternatively, the surface can be wet with a hose and then rolled plastic sheets placed on top. Periodically the slab will have to be re-wet. There are other options as well. Contact your CTS Cement representative for additional information.