The Expanded Shale Clay and Slate Institute (ESCSI) Stays In Step with Sustainability

By John Ries, ESCSI

The Expanded Shale, Clay and Slate Institute (ESCSI) is actively involved nationally at ACI and ASTM in developing four documents that show how expanded shale, clay and slate lightweight aggregate optimizes the sustainability of concrete.

ESCSI has been instrumental in getting the internal curing section 2.7 of ACI 130 Sustainability Document written and balloted to the materials subcommittee and to ACI 130 main committee. The section covers definitions, benefits, economics, environmental, social and concludes with the following:

“Internal curing using lightweight aggregate is a practical and economical way of supplying additional water for curing throughout the concrete mixture. Internal curing offers benefits of improved hydration and reduced early-age cracking, which helps concrete achieve its maximum potential as a sustainable building material by extending its service life. Use of lightweight aggregate in this manner is not a substitute for optimization of other procedures such as mixture proportioning, placement practices, and curing procedures prescribed for ordinary Portland cement concrete.”

ACI 213 Guide for Structural Lightweight-Aggregate Concrete has added a 22-page section titled, Enhanced Performance Due to Internally Stored Water (Internal Curing). The section includes the following sub-sections and summary:

  • Concept of Internal Curing
  • Mixture Proportioning For Internal Curing
  • Properties of the Aggregate For Internal Curing

  • Influence of Internal Curing on Concrete Properties and
  • Behavior
  • Effect of Internal Curing on Plastic Shrinkage
  • Effect of Internal Curing on Concrete Strength
  • Effect of Internal Curing on Elastic Modulus
  • Effect of Internal Curing on Elastic Modulus
  • Effect of Internal Curing on Creep
  • Effect of Internal Curing on Volume Change and
  • Cracking
  • Effect of Internal Curing on Porosity
  • Effect of Internal Curing on Fluid Transport
  • Field Experience
  • Internal Curing Summary and Potential Impact on
  • Sustainability (The following quote from the
  • document has been approved by the committee and
  • will now be reviewed by the ACI technical action
  • committee (TAC).

“Mixtures with internal curing show similar or improved mechanical properties, reduced risk of cracking, and the reduced chloride ingress. The additional costs of concrete with internal curing are estimated to be between 0 to 14% of the materials cost.Internal curing may require additional quality control and aggregate management. With time and increased familiarity with internal curing it is expected that new opportunities will rise to use internal curing.

Internal curing is just one of the many tools that may be able to increase the sustainability of concrete < elements. Internal curing has the potential to improve the durability and reduce the life-cycle costs of concrete structures. Cusson et al. (2010) compared the service lives of theoretical high-performance concrete bridge decks with and without internal curing. The high-performance concrete deck without internal curing was assumed to exhibit early-age autogenous and thermal cracking. The high-performance concrete with internal curing was assumed to not exhibit such early-age cracking and provided a further 25% reduction in the expected diffusion coefficient. Based on these and other assumptions, service life estimates of 22 years for conventional concrete, 40 years for high-performance concrete without internal curing, and 63 years for high-performance concrete with internal curing were obtained. In this case, internal curing should produce a bridge deck with an increased service life and a significantly reduced life cycle cost.”

Committees ACI 308/213 are jointly developing the Report on Internally-Cured Concrete Using Preconditioned Absorptive lightweight Aggregate. This 36-page report has been in the works for several years and has just been approved by the 308 committee. It will now be balloted to the 213 committee.

ASTM C9.21, Proposed Standard Specification for Lightweight Aggregate for Internal Curing of Concrete. This is a new 20-page standard has been balloted at the sub committee and will now go out for concurrent sub and main committee ballot. Having an ASTM standard adds credibility to the IC process as well as gives the designers a sense of assurance when designing and specifying IC mixtures.