Laser Diffraction Analysis of NIST 114q Cement per AASHTO Standard T353-14

Laser diffraction analysis of cements is a common industry practice to control quality of cements. Typically, companies must invest in multiple instruments at as many stations. The LISST-Portable|XR is truly portable – the only such instrument worldwide. One instrument can be used for multiple stations, maintaining consistency of results, thus affecting economy.

To demonstrate the suitability of the LISST-Portable|XR, we examine a US National Institute of Standards and Technology (NIST) standard cement powder.

The American Association of State and Highway Transportation Officials (AASHTO) established standards for measuring the size distribution of Portland cement using laser diffraction. The need for this standard had been indicated by US National Institute of Standards and Technology (NIST). NIST had earlier held a round robin (Intercomparison) of laser diffraction systems made by different manufacturers. The results (NISTIR 6931) were disparate due, in large part, to the use of different refractive indices by the different companies. This lead AASHTO to standardize specifications for the real and imaginary refractive index for cement, and a real refractive index for isopropyl alcohol, which is used in wet analysis.

This AASHTO standard [AASHTO T353-14] is important for industry since a major factor in the strength of concrete is the particle size distribution of cement (see here), so that it must be measured accurately. The standard specifies (i) the complex refractive index to be used for the particles, 1.7 + 0.1i , (ii) a refractive index of 1.378 for isopropyl alcohol (IPA) that may be used for wet analysis; and (iii) the sizes where the cumulative size distribution is to be reported. To conform with this AASHTO standard, a corresponding light scattering matrix was computed by Sequoia and incorporated into our LISST-Portable|XR instrument. This permits results according to AASHTO standard.

In the figure above, we show the cumulative size distribution as measured by the LISST-Portable|XR (blu) and as specified by NIST for powder 114q(red). Two black lines show the permitted variability in NIST specification.

The near-perfect agreement between NIST specification of PSD and our reported PSD from the LISST-Portable |XR validates the instrument results. The small deviations from the specified PSD of cement are within tolerance specified by NIST [Table 7, NIST Special Publication 260-166, and Addendum, Table 4].

The typical time for sample preparation, acquisition and processing of such data is less than ~5 minutes.

The LISST-Portable |XR is an excellent tool. Being truly portable, just one can be used at multiple stations in a single plant, or across multiple plants.

11 AUGUST 2017