May Meeting Recap
We had a boisterous crowd on hand for our May Lunch Meeting. All were entertained by GRACE Regional Technical Services Manager, Jason Wimberly who gave us a presentation on Controlled Low Strength Material (CLSM), The Material, The Myth and The Legend. Jason laid out an agenda that covered some basics on what CLSM is and some history on where it originated, some of the engineering properties, both plastic and hardened; and some applications, features and benefits.
ACI Document 229R Controlled Low-Strength Material defines CLSM as; “a self-consolidating cementitious material used primarily as a backfill as an alternative to compacted fill”. Some notable points from ACI 229R include: intended compressive strengths are 1200 psi or less, most applications require 300 psi or less and hand excavatable material should be less than 100 psi. Low density CLSM is preferred when reduced dead loads are critical and is typically 20 to 120 pcf. One of the biggest myths about CLSM is that it is a low strength concrete; CLSM is not concrete and should not be specified as such. Most of the ASTM Standards that govern CLSM are D designation standards (soil) and not C designation standards (concrete). CLSM has been around since the early 1970’s as a replacement for poorly compacted soil, first produced primarily with cement, fly ash, sand & water. Today, approximately 10 million cubic yards are placed annually with most applications requiring future excavation (100 psi strength or less).
The primary plastic property is flowability. CLSM must be self-leveling and self-compacting without material segregation or subsidence (hardened volume change due to water displacement, generally less than 1/8 inch per foot of depth). Hardening time, length of time required to support the weight of a person, is dependent on the CLSM constitute materials and is generally between 1 and 5 hours. Some typical hardened properties include:
• Density: 115 to 145 pcf, 90 to 100 pcf with AEA & 20 to 120 pcf for LD-CLSM
• Excavatable: by Hand less than 100 psi, by machine less than 300 psi, or non-excavatable greater than 300 psi.
• Settlement: CLSM should not settle like compacted fill
• Shrinkage: what can be thought of as normal concrete shrinkage does not affect CLSM performance
• Corrosion Potential: can be measured using the same electrical resistivity methods commonly used for evaluating soil
• Thermal: insulation and conductivity, conventional CLSM is generally not a good insulator, LD-CLSM with high air contents may exhibit good insulating properties
• Permeability: similar to compacted granular fills, typically in the 10-4 to 10-5 cm/sec range
Jason closed with some typical mix design examples, common applications and a few case studies; his complete presentation is attached here. Vice-President, Wilbur Bragg, closed the meeting by thanking everyone for their attendance, wishing them a safe and happy summer break and making the GA Chapter Speaker’s travel mug presentation.