Concrete
Chemistry and DurabiltyConcrete
Chemistry and Durabilty
Our research in high performance concrete emphasizes improving durabiltiy through increased chemical resistance to deleterious reactions. We base our approach on the application of mineralogical and geochemical principles and techniques to the study of concrete. Concrete strength and durability arise from the binding of aggregate materials (rock and sand) by hydrated cement phases (known as CSH gels). The stability of the CSH-rock system controls the durabilty of concrete and depends on favorable pore fluid chemistry. In other words, concrete durability depends on controlling fluid-rock reactions, and is therefore uniquely suited to the application of geochemical methods which have long focused on fluid interactions with rock materials. Other areas of research include understanding the behavior of pozzolanic materials in concrete, the development of an in situ geophysical probe to evaluate the nature and extent of fractures and deleterious reactions, and the development of improved field evaluation methods for the identification and study of deleterious reactions. For more information contact George Guthrie (gguthrie@lanl.gov) or Bill Carey (bcarey@lanl.gov). Also see Recent Press for the Concrete Program.
A common deleterious
reaction in concrete is the alkali-silica reaction (ASR) in which the concrete
pore fluids attack the aggregate and produce a swelling, alkali-silica
gel. This image shows the characteristic map cracking that can develop
when ASR occurs in a concrete pavement. This cracking can seriously degrade
a concrete pavement in as short as 5-10 years.
We're investingating
several geochemical and mineralogical issues related to ASR. ASR results
from an interaction between silica-rich materials in the aggregate, the
Ca-Si-rich materials in the cement paste, and the pore fluid. This reaction
results in the formation of a swelling gel, whose presence in this SEM
image can be recognized by the dessication cracks.
ASR is often detected
using a test involving uranyl acetate (as shown in the Figure, where ASR
is shown by the yellow-green). We've developed an improved method of identification
of ASR using geochemical labeling techniques. The new method is easy to
use, is visible in normal light, and allows mapping and a detailed investigation
of the extent and origin of ASR
George
Guthrie and Bill Carey apply newly developed stains for the identifcation
of the alkali silica reaction to a core of concrete taken from a bridge
in Albuquerque, NM. See the recent press
release.