CRC JOINTCAST

Joints that are small, strong and simple

A SOLUTION FOR CONNECTING ELEMENTS

As a manufacturer of prefabricated elements, it is crucial for us to have an effective solution for connecting the elements. The joints must be short, simple, and at least as strong as the elements being connected.

This allows us to divide the structure into smaller parts in the most practical way regarding transport, assembly, and handling on-site and at the factory, as well as reducing the costs of the molds. Examples include complicated staircases such as the Per Aarsleff project or projects like the Catharina Bridge, where element size was chosen without constraints.

For the staircase, straight Ø16 mm reinforcement bars were connected with a 100 mm joint, and for the Catharina Bridge, a 550 mm joint was used for Ø25 mm reinforcement bars.

Spiral staircase during installation - and after..

CRC JOINTCAST - A DRY MORTAR USED ON-SITE

This is made possible by using CRC JointCast - a dry mortar similar to CRC i2®, which we use in the factory. CRC JointCast comes in small bags, so only water and steel fibers need to be added when the mortar is mixed on-site. The fiber content in CRC JointCast is slightly higher than in our other mixes to ensure that we can achieve full anchorage with a bond length of 5-10 times the reinforcement diameter.

This combination of a very high steel fiber content, which provides toughness and high tensile strength, with a concrete that is strong and has dense packing with very fine particles, ensures excellent adhesion to the reinforcement bars. Since the strength development is very rapid (120 MPa in 3 days), it is often possible to achieve full capacity in a joint within a few days.

Catharina Bridge – ready for casting joints, and the finished bridge: [Gerda van Ekris]

EARLY APPLICATIONS

CRC JointCast was developed in the late eighties and early nineties, and the first projects were completed in 1995. The first major project involved two new buildings for Aalborg University (a total of 15,000 m²), where CRC JointCast was used to connect flat slabs, so the finished system functioned as a continuous slab cast on-site. Other applications included bridges, extension of columns and beams, joints of load-bearing walls, or simply for repair or retrofitting. Since the joints are small, only 3 m³ of CRC JointCast was needed to add an extra lane to a 100-meter bridge in a project in Odense, Denmark.

The bridge connections were further developed in a project at Chalmers University, where the joints were designed to be easily formworked at the bottom. The nominal joint width in the experiments was 100 mm for Ø16 mm bars, but the bond length in some of the experiments was as low as 65 mm. In these experiments, full capacity was also achieved, and in both cases, the joint was designed to be at least as strong as the elements on either side of the joint.

A conventional joint at the top and a CRC joint below

APPARENTLY A WELL-KEPT SECRET!

CRC JointCast has been available on the market since 1995—but apart from the previously mentioned applications, its main use today is actually in our own products. It has been difficult to pinpoint areas where a material of this type provides the greatest benefit, so it is currently used to connect stairs, bridges, and large beams and columns, but as mentioned, mostly for our own projects. Others might be inclined to think that this is because we want to keep knowledge of this type of joint to ourselves—to give a competitive advantage in our projects—but that is not the case. We are simply not very good at marketing and selling CRC JointCast! Part of the challenge is identifying construction systems or projects where this type of joint system can benefit contractors and prefabricated producers by making installation easier and the final product more durable. This could change, however, if some of the methods developed in North America for bridges begin to be applied in Europe as well.

In North America, more than 200 bridges have been produced with this type of joint system over the last 7-8 years, and Ben Graybeal and his group at the Federal Highway Administration have published extensive reports on cast-in-place UHPC joints between prefabricated bridge elements:

https://www.fhwa.dot.gov/research/resources/uhpc/publications.cfm

The benefits of this system will hopefully also be recognized for projects in Europe eventually—and when they are, we will be ready with the perfect joint material—and we will make sure it is no sec