Ultra High Performance Concrete Without Silica Fume
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Solution Overview
Problem
Existing concrete compositions rely heavily on pozzolanic silica fume for high compressive strength and setting properties, but there is a need to replace silica fume with non-pozzolanic materials while maintaining or exceeding these properties, particularly in ultra-high performance concrete, and achieving a shorter setting time.
Innovation Solution
A concrete composition that substitutes silica fume with non-pozzolanic materials like ground limestone or precipitated calcium carbonate, combined with specific sand gradations and water-reducing superplasticizers, to achieve compressive strengths greater than 100 MPa without silica fume, along with reduced shrinkage and a shorter setting time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If silica fume is used as an additive in cement, then compressive strength is improved, but setting time is prolonged
Solution Approach 1:
The patent changes the chemical composition parameters by replacing silica fume with non-pozzolanic materials like ground limestone and precipitated calcium carbonate. This substitution fundamentally alters the chemical reactions in the cement matrix, eliminating the delayed setting effect while maintaining compressive strength through alternative mechanisms such as particle packing and nucleation effects.
Solution Approach 2:
The patent employs readily available, inexpensive non-pozzolanic materials (ground limestone, precipitated calcium carbonate) as substitutes for silica fume. These materials are more accessible and can be processed more quickly, thereby reducing both material cost and setting time while achieving the required mechanical properties.
2Loss of time
If silica fume is replaced by non-pozzolanic material, then setting time is shortened, but compressive strength may be reduced
Solution Approach 1:
The patent creates a composite concrete system combining non-pozzolanic fillers (ground limestone, precipitated calcium carbonate) with optimized sand gradations and superplasticizers. This composite approach compensates for the lack of pozzolanic activity through synergistic effects: the fine particles fill voids, the superplasticizer ensures proper dispersion and workability, and the sand gradation optimizes packing density, collectively maintaining high compressive strength despite the absence of silica fume.
Solution Approach 2:
The patent applies local quality optimization by carefully controlling the particle size distribution and surface properties of the non-pozzolanic materials. The ground limestone and precipitated calcium carbonate are processed to specific fineness moduli and surface areas, creating locally optimized zones within the concrete matrix that enhance early strength development and overall mechanical performance without requiring pozzolanic reactions.
3Strength
If silica fume is used, then adequate compression resistance is achieved, but the concrete requires thermal curing for high strength
Solution Approach 1:
The patent enables the concrete to achieve high compressive strength through self-service mechanisms inherent in the non-pozzolanic material system. The ground limestone and precipitated calcium carbonate, combined with optimized water-cement ratios and superplasticizer formulations, allow the concrete to develop strength through conventional curing processes without requiring external thermal energy input, thereby eliminating the need for energy-intensive thermal curing cycles.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The concrete composition achieves compressive strengths of over 100 MPa, preferably greater than 120 MPa, with a shorter setting time and reduced shrinkage, even without thermal curing, while eliminating the need for silica fume, making it suitable for high-performance applications.
Implementation Method 1
A pozzolan is described in Lea's Chemistry of Cement and Concrete, 4th edition, published by Arnold as an inorganic material, natural or synthetic, which hardens in water when mixed with calcium hydroxide (lime) or with a material which can release calcium hydroxide (such as Portland Cement clinker). A pozzolan is generally a siliceous or siliceous and aluminous material which, alone, possesses little or no cementitious value but which is capable, in the presence of moisture, of reacting chemically with calcium hydroxide at ambient temperature to form compounds having cementitious properties.
Implementation Method 2
water-reducing superplasticizers, to achieve compressive strengths greater than 100 MPa without silica fume, along with reduced shrinkage and a shorter setting time
Data Source
AI summary
The invention provides a ultra high performance concrete (UHPC) which comprises in parts by weight: 100 of Portland cement; 50 to 200 of a sand having a single grading with a D10 to D90 between 0.063 and 5 mm, or a mixture of sands (preferably two sands), the finest sand having a D10 to D90 between 0.063 and 1 mm and the coarsest sand having a D10 to D90 between 1 and 4mm 10 to 50 of a particulate substantially non-pozzolanic material having a mean particle size less than 15 &mgr;m; 0.1 to 10 of a water-reducing superplasticizer; and 10 to 30 of water; which concrete is substantially free of silica fume; the said concrete having a compressive strength greater than 100 Mpa at 28 days.