Nonconventional Concrete Technologies Renewal of the Highway Infrastructure (1997) / Chapter Skim
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2 Controlled Synthesis of Potential Matrix Materials and Reactive Additives
2 Controlled Synthesis of Potential Matrix Materials and Reactive Additives
Pages 39-52
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From page 39... ...
Some possible combinations of these three strategies to produce a nonconventional matrix and potentially resolve some of the shortcomings of conventional concrete matrices are: . An energy efficient and environmentally benign strategy to produce matrices that incorporate waste materials (e.g., ground glass, blast-furnace slag, fly ash, silica fume)
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From page 40... ...
GELATION AND RHEOLOGY CONTROL Improved methods for controlling the setting process of conventional concrete are essential to proclucing nonconventional concretes with superior properties and performance. Theoretical and experimental advances over the past 10 years have shown that virtually all gels fall into the same universality class, which means that the funclamental physics of these gels is inclepenclent of the length scale of the gel's internal structure.
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From page 41... ...
On the microscopic level, this transition occurs when a random growth process on either a molecular or colloidal scale generates a so] of clusters with a fractal structure.
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From page 42... ...
on colloidal gels, the principle of universality ant! the fact that the mechanical properties of a concrete body are the same as for the colloidal gel mean that a conventional concrete structure will be transformer!
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From page 43... ...
It is no coincidence that the current additives called "high-range water reducers," which can make concrete workable at much lower water-to-cement ratios, are surfactants. Surfactants work by preventing either the formation of fractal clusters or their percolation.
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From page 44... ...
Potential methods for water ant! shrinkage control include the addition of synthetic polymers ancl cellulose derivatives, wood and paper waste materials, swelling clays, and high-range water reducers.
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From page 45... ...
Recyclecl paper pulp that is no longer suitable for paper formation is a relatively inexpensive source of organic material. A potential risk of using organic materials is that they tend to decompose.
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From page 46... ...
The clays wouIcl then react in the later stages of the setting process to become part of the matrix and ensure a good pre-structure for clurability. Although these clays have proven to be unsuitable for conventional concrete, rheological studies have shown that they can counteract self desiccation and increase dispersion of silica fume, for example (Henrichsen, 19951.
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From page 47... ...
In large pourings, the heat released can raise temperatures to levels at which unwanted side-reactions occur. Given the large thermal expansion coefficient of water, thermal gradients cause differential expansion during the exothermic setting process and thermal tensile stresses during final cooling, both of which cause stress cracking.
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From page 48... ...
REACTIVE INORGANIC ADDITIVES Many inorganic substances (e.g., fly ash, silica fume, blast-furnace slag) have been incorporated as "additives," or supplemental cementitious materials, in cement mix designs.
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From page 49... ...
REBAR CORROSION CONTROL AGENTS The ancillary role that conventional cement plays in passivating the rebar poses some significant challenges for a nonconventional cement. As stated in Chapter 1, the calcium hyciroxicle component that generates the high-pH conclitions and prevents the rebar from corroding also tends to dissolve rather rapidly under natural water conditions.
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From page 50... ...
Substances such as sulficle ores or blast-furnace slags could create a sufficiently reducing environment to reduce the rate of rebar corrosion. Organic materials (e.g., sawdust, paper pulp, polymers)
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From page 51... ...
Increased unclerstancling of these linkages might make it possible to develop such new technologies as crystalline or macromolecular nucleating agents. The adclition of nuclei to conventional Portland cement at key points in its synthesis might make it possible to control the incubation time of setting, improve the spatial and temporal homogeneity of the material, or crystallize the gel phase into more chemically clurable phases.
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From page 52... ...
in ambient aqueous conditions. Thus, novel strategies for the design and synthesis of nonconventional concrete materials couIcl potentially be developer!
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