DSP materials

Densely packed cementitious materials are commonly also called also DSP materials, which is an acronym for Densified Systems containing homogeneously arranged ultrafine Particles. The alternative term reactive powder concrete is also used. In principle these are cementitious materials formed by the Itydration of densely packed particles of an inoiganic binder in combination with ultrafine particles of a second, less reactive or non-reactive filler. Some additional particulate materials may also be present. 

Silica fume (microsilica) is the ultrafine material most commonly used in making DSP materials. Its main functions are ... 

Typically, the silica fume/cement ratio in DSP materials is about 0.20-0.25. This ratio corresponds to the best space-filling performance, but it is too high for a full conversion of the silica fume to C-S-H in a pozzolanic reaction. 

Besides microsilica, other ultrafine materials may be used as constiments of DSP systems, as long as their particles are small enough to fill the existing spaces left between the particles of cement. Aldridge et al. (1992) produced a DSP material using ultrafine mtile (TiOj) instead of microsilica as filler. The resulting material had properties comparable to those of a DSP product made with microsilica, in spite of the absence of a pozzolanic reaction in this combination of starting materials. 

Figure 14.1 Effect of medium-size particles on compressive strength of DSP material. Mixing ratio cement microsihca medium-size particles=7 1 2. FA, fly ash PSA, paper sludge ash BX=calcined bauxite GBFS= granulated blast furnace slag.

The appropriate water/solid ratio in producing DSP materials ranges between about 0.12 and 0.22. Under these conditions a dense but fairly fluid paste is obtained, thanks to the combination of an optimum particle size distribution of the solids that are present and the chemical action of the dispersant. 

As for the cement, most of the silica fume remains non-reacted, and does not undergo a pozzolanic reactiom In one particular case only 20% of the cement and 9% of the silica fume had been consumed within 28 days of hydration at 20°C (Zanni et al., 1996). These low degrees of reaction must be attributed to the very low water/solid ratios employed in producing DSP materials. 

Because of the low initial water/sohd ratio the cumulative pore volume of hardened DSP materials is significantly reduced. At the same time there is a shift to smaller radii (Touse, 1989 Cheyrezy et al., 1995). Both factors affect favorably the strength properties and the permeability of the material. 

The following may be considered to be typical physico-mechanical properties of DSP materials (Richard and Cheyrezy, 1995) DSP materials cured at ambient temperature or heat-treated at temperatures below 90 °C, produced without application of mechanical pressure ... 

DSP material exposed to mechanical compaction and heat treated at 250-400 °C... 

It has been suggested that DSP mixes should be employed instead of high-performance concrete (Richard and Cheyrezy, 1995). Because of the high ductility of DSP material its... 

The application of DSP materials extends beyond building construction to heavy duty industrial floors and mechanical parts. The service life of elements... 

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