DE102008031852A1 - Stability and density optimizing method for cement stone matrix of concrete, involves determining reference value of compression strength and pore structure based on concrete, and determining minimum water film thickness of specific value - Google Patents

Abstract

The method involves determining a reference value of compressive strength and pore structure at a base concrete. A packing density of the base concrete is determined. An output water film thickness is determined on the basis of packing density and granulometry with water content of the base concrete. Another reference value of compression strength and the pore structure are determined based on a concrete according to determined film thickness. A minimum water film thickness in the range of 0.001 and 0.3 micro meter is determined.

Description

The The present invention relates to a method for optimizing the Strength and tightness of the cement stone matrix of a concrete.

Of the Concrete as a construction material essentially presents itself as a ternary system consisting of the binder cement, water and an aggregate. Due to the reaction of the cement with the water, the strength-forming C-S-H-phases. It is known, by adding reactive fines, so-called additives such as silica dusts, fly ash etc. either to further increase the strength of the concrete, or save cement at the same strength values. By the addition of such reactive fines, the cemented stone matrix is replaced by a Reaction product of water and cement as well as reactive fines with a diameter <0.125 mm strength-promoting influenced.

Known is also the diffusion and penetration resistance of a concrete against liquid, water and concrete attacking liquid, such as z. As sulphate-containing solutions or acids characterized to increase that ratio between water and cement (w / c value) is reduced. That is, through a reduction of the water content can be an increase Diffusion and penetration resistance to gases, water and other concrete attacking liquids can be achieved.

As already discussed elsewhere is known by the Addition of reactive fines the strength of the cement stone matrix To increase, therefore, the strength of the concrete as a whole. It is known in this context, the cement always the same Parts by weight to replace the reactive additive, wherein but only a very specific proportion of the additive may be counted as cement equivalent. When fly ash (pozzolanically reactive fines) may, for example only 40% by mass of the used fly ash are counted, while the highly reactive silica fume 100 percent by mass can be counted.

adversely when using reactive substances, in particular silicate dust, is that these reactive substances when they replace cement to 100% can, are relatively expensive. Fly ash is comparatively cheap, but it may only - as stated above - until to 40% by mass of the used fly ash.

From the US 5,527,387 A In this respect, a concrete is known which has a composition of proportions of cement, sand, coarse aggregates, water, fly ash, water reducers, air entraining agents and fillers in order to produce specific mass fractions the concrete mixture with a certain compressive strength, slump and minimum cost. It is essential here that, in turn, reactive substances, in particular fly ash and silica fume, are used.

From the US 2006/0287773 A1 For example, a method of optimizing concrete compositions with a computerized method is known which calculates a variety of compositions and tests them virtually in terms of strength. Here, a so-called K factor is introduced. However, in this case the packing density is only calculated two-dimensionally, whereby it can not be determined exactly how the cavities can be filled. The method also has the disadvantage that it is very expensive.

at The development of ultra-high strength concrete, UHPC concrete, has become demonstrated that the tightness and strength of cement stone thereby can increase that the packing density of the fine grain is optimized so that the remaining between the solid Cavity is minimized.

Except In this context, however, the influence was left out the water film thickness and the specific surface area the packing density to be achieved and thus the properties of the concrete.

• 1. Bestimmung der Korngröße des Bindemittels (Zement) eines Ausgangsbetons mit einer Gesteinskörnung;
• 1a. Bestimmung der Zwischenräume zwischen den Zementkörnern;
• 1b. Bestimmung der Wasserfilmdicke des Ausgangsbetons durch Bestimmung des Feinstoffgehalts aus der Gesteinskörnung; Bestimmung der Granulometrie des Zements und des Feinstoffs aus der Gesteinskörnung; Bestimmung der Packungsdichte des Ausgangsbetons; Bestimmung der spezifischen Oberfläche des Gemisches aus Zement und Feinstoff der Gesteinskörnung bei vorgegebener Wassermenge;
• 1c. Bestimmung von Referenzwerten am Ausgangsbeton, wie Druckfestigkeit und Porenstruktur;
• 2. Rechnerische Bestimmung einer Packungsdichte durch volumengleichen Packungsdichte oberhalb der des Ausgangsbetons liegt;
• 2a. Bestimmung der Ausgangswasserfilmdicke anhand der Packungsdichte und Granulometrie mit dem Wassergehalt des Ausgangsbetons.
• 2ab. Bestimmung der Referenzwerte von Druckfestigkeit und Porenstruktur anhand eines Betons gemäß 2a;
• 2b. Festlegung einer Mindestwasserfilmdicke im Bereich von 0,001 μm und 0,3 μm;
• 2c. Bestimmung von Referenzwerten für Druckfestigkeit und Porenstruktur aus einem Beton gemäß 2b;
• 3. Aufstellen einer Funktion anhand der Werte von 2ab. und 2.
• 4. Durchführung der Schritte 2. bis 3. für jeden gewünschten reduzierten Zementgehalt.

In order to take into account now the water film thickness and the specific surface area in the production of a concrete to optimize the strength and density of the cement paste matrix of such a concrete, the following process with the corresponding process steps is proposed:

• 1. Determination of the grain size of the binder (cement) of an initial concrete with an aggregate;
• 1a. Determination of the spaces between the cement grains;
• 1b. Determination of the water film thickness of the starting concrete by determination of the fines content of the Aggregate; Determination of granulometry of cement and fines from the aggregate; Determination of the packing density of the starting concrete; Determination of the specific surface area of the mixture of cement and fines of the aggregate for a given amount of water;
• 1c. Determination of reference values on the initial concrete, such as compressive strength and pore structure;
• 2. Computational determination of a packing density by volume equal packing density is above the Ausgangssbetons;
• 2a. Determination of the initial water film thickness on the basis of the packing density and granulometry with the water content of the starting concrete.
• 2ab. Determination of the reference values of compressive strength and pore structure using a concrete according to 2a;
• 2 B. Establishing a minimum water film thickness in the range of 0.001 μm and 0.3 μm;
• 2c. Determination of reference values for compressive strength and pore structure from a concrete according to 2b;
• 3. Establish a function based on the values of 2ab. and 2.
• 4. Perform steps 2 to 3 for any desired reduced cement content.

d_w

Wasserfilmdicke [μm]

V_w

Wasservolumen [dm³]

V_H

Volumen Hohlraum [dm³]

PD

rechnerische Packungsdichte nach Schwanda [-]

s_vf

spezifische Oberfläche der Feststoffe [dm²/dm³]

V_f

Volumen der Feststoffe [dm³]

It is essential in the method according to the invention that in calculating the packing density and the water film thickness, the space around each grain, that is, by calculating the three-dimensional cavities, cement is replaced by inert fines, in a form that allows the cavities be filled in a given volume between the individual cement grains by the addition of inert fines, in which case the water film thickness is reduced. The determination of the water film thickness (initial water film thickness) on the basis of the packing density and the granolometry with the water content of the starting concrete is carried out according to the following formula:

d _w

Water film thickness [μm]

V _w

Water volume [dm ³ ]

V _H

Volume cavity [dm ³ ]

PD

mathematical packing density according to Schwanda [-]

s _vf

specific surface area of the solids [dm ² / dm ³ ]

V _f

Volume of solids [dm ³ ]

One another essential feature here is that the inert fines, which are provided as fillers, at least 4.3 times as are fine as the cement, with the fine cement fines up to be twice as coarse as the cement. By such a volume equal Replacement of the cement by such inert fines under consideration the water film thickness and the packing density may have the characteristics of the concrete, in particular with regard to its compressive strength and Tightness, despite a cement reduction either kept the same or even improved.

Based of the figures, the invention will be exemplified in more detail below explained.

1 shows in case 1 a mixture of coarse ground grains and a few small grains;

2 shows in case 2 a mixture of fine basic grains and a few large grains;

3 shows a diagram for calculating the factors of void content for k ₀ = 0.6;

4 shows a diagram of the behavior of cement paste resistance to the water film ceiling.

To explain the procedure, the following should be noted:
The determination of the grain size of the binder may, for. B. by using a laser diffraction granulometer.

S, s

Festraum einer Ansammlung von Körnern

H, h

Hohlraum eines Korngemisches im eingerüttelten Zustand

K, k

Hohlraumgehalt eines Einkornstapels

V

aus Festraum und Hohlraum bestehender Gesamtraum einer Ansammlung von Körnern im eingerüttelten Zustand: V = H + S bzw. V = K + S

The determination of the spaces between the individual cement grains is calculated according to Schwanda / Reschke [ Schwanda, F .: The mathematical method for the determination of the cavity and cement paste of aggregates and its importance for prestressed concrete, cement and concrete 37, 1966, p. 8-17 ; Reschke T .: The influence of the granolometry of the fines on the microstructure development and the strength of concrete, series of the cement industry, Issue 62/2000, Bau + Technik Verlag, Dusseldorf 2001 ]. First of all, the following parameters have to be defined, which are important for the determination of void content according to Schwanda:

S, s

Festival room of a collection of grains

H, h

Cavity of a grain mixture in the shaken state

K, k

Void content of a Einkornstapels

V

From the fixed space and cavity existing total space of an accumulation of grains in the shaken state: V = H + S or V = K + S

The capital letters S, H, K, V indicate the volume in the unit of measure. The lowercase letters s, h, k, v represent the relationship between S, H and K and the solids of all the grains forming the mixture or the Einkornstapel: s = S: ΣS h = H: ΣS k = K: S

The method described is based on the behavior of packed particles of different sizes. A distinction is made between a basic grain and the considered Beikorn, which is to fill the cavities of the basic grain package. There are two cases to be distinguished. In the first case, the particle volume of the bees grains is less than or equal to the void volume of the base grain package, whereby the total volume of the mixture does not change. It only reduces the cavity around the fixed space of the fine Beikörner. The coarse component is referred to as the basic grain x _s . 1 illustrates this process vividly, in which a mixture of coarse ground grains and a few small grains is shown there.

The calculation is done as follows:

Note that at h _{g, f} (Case 1), the first of two pointers (as a designation in a function) always refers to the fundamental grain. This approach remains valid until the smaller grains have filled in the gaps between the coarse grains without dislodging them.

If, on the other hand, the set of _{Sf is increased} beyond this limit, another context applies, for the presentation of which one arrives at a collection consisting only of very fine grains. For this second case ( 2 ), the proportion of the fine components is greater than the void content of the large, so that the coarse grains are forced apart and the total volume increases accordingly. The void content of the mixture is then equal to the void content of the fine component, which is why in this second case, the fine component is referred to as the basic grain x _s .

The result is the following approach:

For the calculation of the void content of mixtures of two grains, two formulas are thus obtained. The one that always returns the value for h is always valid. Both formulas give the same value, the ratio S _g : S _{f was} found which has the lowest void content that can be achieved with the given grain.

So far It was assumed that the diameter of the coarse grains is many times larger than the diameter of fine grains.

However, if this size ratio falls below a certain limit, the finer grains can no longer readily disappear into the voids between the larger grains, but must crowd them apart. Thus, between the cases 1 and 2 described above, there is a transition region in which the grains obstruct each other and partially force the basic grain framework apart. As a result of this particle obstruction occurs an increase in volume and thus an increase in the void content, since the värmmutomindernde influence of Beikorns decreases. This is to be considered by a factor a. The a-values depend once upon the shape and surface finish of the grains and also on the ratio of the diameter of the coarser grains to that of the finer ones. If both grains have the same diameter, then a = 0. The range of those proportions of the components, in which this particle obstruction is noticeable, is therefore called the range of particle disability w. The range w depends on the ratio of the basic grain x _s to a limit grain size x _w , at which no particulate hindrance occurs anymore. Due to the range of the particle hindrance, the influence of the grain shape or the size ratio is taken into account. Calculated is the possible increase in the total volume of the particle mixture.

In addition to the particle size distribution, parameter values are needed to take into account the influences of the particle shape and surface roughness of the particles as well as the range of particle hindrance. This description of the type of material is made via the parameter k ₀ , which indicates the void fraction of the single-grain bed and the range of the particle obstruction w ₀ .

mit:

k₀:

Hohlraumanteil Einkornschüttung

ε:

Hohlraumgehalt [Vol.-%]

D:

Packungsdichte

The void fraction is determined according to the following formula:

With:

k ₀ :

Void content of single-grain bed

ε:

Voids content [vol.%]

D:

packing density

mit:

w:

Reichweite der Teilchenbehinderung

x_w:

Grenzkorngröße

x_s:

Grundkorngröße

With the range of the particle obstruction, the size ratio of the basic grain is determined to a marginal grain. This value can be estimated by the following relationship:

With:

w:

Range of particle obstruction

x _w :

Grain size limit

x _s:

Basic grain size

One low value for the particle obstruction w results for a small ratio between the grain groups, whereby a particle obstruction in the form of a divergence takes place.

By the void content of the Einkornschüttung k ₀ and the range of the particle disability w, one can characterize the different grains by number according to their type so that the void content of any mixture can be calculated with sufficient accuracy. The two parameters k ₀ and w are determined by simple experiments. They can be estimated with some experience but also for most purposes with sufficient accuracy.

The void fraction of fine individual fractions is assumed to be k ₀ = 0.82 (45 vol.% Void), the range of particle disability w = 2. The math used in the model matic relationship between k ₀ , w, the grain size ratio of basic grain x _s to the respective Beikorn x _i and the factor a _{s, i} as a function of the aforementioned variables, is exemplary of the parameters k ₀ = 0.6 in 3 shown. The correlation between the parameters and the factor a _{s, i} was determined by experiments in Schwanda and according to Reschke in 3 generalized for k ₀ = 0.6.

h_s

Hohlraumanteil Grundkornklasse

k₀

Hohlraumanteil Einkornschüttung

a_s,i

Faktor a (Teilchenbehinderung) der Kornklasse i

s_i

Festraumanteil Kornklasse i am Gesamtfestraum

Based on the in 3 shown correlations, the void fraction of the respective basic grain class h _{s was} determined. This is obtained by reducing the void content of the basic grain k ₀ by the corresponding solids content of the pickle of all other grain classes s _i , taking into account the respective valid factor a _{s, i} . H s = k 0 - Σa s, i · s i With:

h _s

Void fraction basic grain class

k ₀

Void content of single-grain bed

a _{s, i}

Factor a (particle disability) of the grain class i

s _i

Festraumanteil grain class i in the total festival room

In turn, each grain class was considered once as a basic grain. The class of grain which delivers the largest void fraction of the basic grain h _{s, max} is decisive for the calculation of the packing density D (or also the degree of density D) of the total particle bedding:

The other calculated cavity fractions h _{s, max} apply to mixtures in which the spaces occupied by individual grain groups intersect each other.

The model according to Schwanda is limited by the fact that the parameters k ₀ and w can only assume a constant value within the calculation. The different nature of the individual fractions of a particle mixture can thus be insufficiently taken into account.

d_w

Wasserfilmdicke [μm]

V_w

Wasservolumen [dm³]

V_H

Volumen Hohlraum [dm³]

PD

rechnerische Packungsdichte nach Schwanda [-]

s_vf

spezifische Oberfläche der Feststoffe [dm²/dm³]

V_f

Volumen der Feststoffe [dm³]

The determination of the water film thickness is made by the calculation according to Krell of the known formula:

d _w

Water film thickness [μm]

V _w

Water volume [dm ³ ]

V _H

Volume cavity [dm ³ ]

PD

mathematical packing density according to Schwanda [-]

s _vf

specific surface area of the solids [dm ² / dm ³ ]

V _f

Volume of solids [dm ³ ]

Of Further, the granulometry of cement and fines is out to determine the aggregate. This happens in the the proportion of fines from the aggregate sieved and then the grain size distribution z. B. by means Laser diffraction measurement (with laser diffraction granulometer) is determined.

The Determination of the packing density of the starting concrete takes place again to Schwanda after the already negotiated formula mechanism. The determination of the specific surface of the mixture from cement and fine material is measured by BET, Blaine or other methods. It is assumed that the Particles are spherical. For the mathematical Determination of the packing density is based on the above-discussed calculation modes referred to Schwanda.

The Determination of the initial water film thickness based on the packing density and Granulometrie done according to Krell as stated above.

For the question of how much of cement is replaced by inert solids with reduced water film thickness will be on the 4 directed.

in this connection be with pre-determined water film thicknesses in the range 0.001 up to 2.0 μm specimens with also previously established fines levels. On these specimens the determination of the compressive strength takes place. These value pairs form the basis for curves that are linear or nonlinear depending on which underlying Dependence the higher accuracy can be achieved can. This method can be used to determine the water film thickness be replaced with the corresponding replacement of the cement by a inert fines have at least the same strength or impermeability can be achieved.

The Values from the water film thickness can be determined by the following Equation into a w / z value (water cement value) are converted.

d_w

Wasserfilmdicke [μm]

s_vF

spez. Oberfläche des Feinstoffs [dm²/dm³]

V_F

Feinstoffvolumen [dm³]

PD_F

rechn. Packungsdichte nach Schwanda [-]

a_Z

volumetrischer Anteil des Zements [-]

ρ_z

Reindichte des Zements [kg/dm³]

On the basis of these values, a customary mixture formulation can be worked out.

d _w

Water film thickness [μm]

s _vF

spec. Surface of fines [dm ² / dm ³ ]

V _F

Fine matter volume [dm ³ ]

PD _F

rechn. Packing density according to Schwanda [-]

a _Z

volumetric proportion of cement [-]

ρ _z

Pure density of cement [kg / dm ³ ]

The method according to the invention will now be explained in greater detail on the basis of examples. component unit Output water cement value w / z ₀ 0.35 0.40 0.50 0.60 aggregate kg / m ³ 1965 eingeschl. Air [dm ³ ] dm ³ / m ³ 15.0 Conventional concrete - without packing density optimization w / z value, effective - 0.35 0.40 0.50 0.60 cement content kg / m ³ 438.9 408.6 358.9 320.0 water content kg / m ³ 153.6 163.4 179.5 192.0 rechn. Water film thickness microns 1.21 0.84 0.66 0.30 Compressive strength after 28d N / mm ² 66.0 60.0 50.0 40.0 Kapillarporengehalt Vol .-% 3.0 4.2 6.8 10.5 Packing density optimized concrete, WITHOUT adaptation of the water film thickness w / z value, effective - 0.44 0.50 0.63 0.75 cement content kg / m ³ 351.2 326.9 287.1 256.0 Quartz flour, pack-effective kg / m ³ 75.1 69.9 61.4 54.7 water content kg / m ³ 153.6 163.4 179.5 192.0 rechn. Water film thickness microns 0.66 0.47 0.38 0.19 Compressive strength after 28d N / mm ² please complete please complete please complete please complete Kapillarporengehalt Vol .-% please complete please complete please complete please complete Packing density optimized concrete, WITH adjustment of water film thickness w / z value, effective - 0.35 0.40 0.50 0.60 cement content kg / m ³ 392.0 367.6 326.9 294.3 Quartz flour, pack-effective kg / m ³ 83.8 78.6 69.9 62.9 water content kg / m ³ 137.2 147.0 163.5 176.6 rechn. Water film thickness microns 0.47 0.32 0.25 0.09 Compressive strength after 28d N / mm ² 76.0 72.0 60.0 50.0 Kapillarporengehalt Vol .-% 2.1 2.6 4.2 5.8

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• US 5527387 A [0006]
• US 2006/0287773 A1 [0007]

Cited non-patent literature

• - Schwanda, F .: The mathematical method for determining the cavity and cement paste of aggregates and its importance for prestressed concrete, cement and concrete 37, 1966, pp. 8-17 [0019]
• - Reschke T .: The influence of the granolometry of the fines on the structure development and the strength of concrete, series of the cement industry, Issue 62/2000, Bau + Technik Verlag, Dusseldorf 2001 [0019]

Claims (3)

Method of optimizing strength and Tightness of the cementitious stone matrix of a concrete with the following Steps: marked by following steps: 1. Determination of the particle size of the binder (cement) an initial concrete with an aggregate; 1a. Determination of the spaces between the cement grains; 1b. Determination of the water film thickness of the starting concrete by determination the fines content of the aggregate; determination granulometry of cement and fines from the aggregate; determination the packing density of the starting ketone; Determination of the specific Surface of the mixture of cement and fines of the aggregate for a given amount of water; 1c. Determination of reference values at the starting concrete, such as compressive strength and pore structure; Second Computational determination of a packing density by volume equal Packing density is above that of the starting concrete; 2a. determination the initial water film thickness based on the packing density and granulometry with the water content of the starting ketone; 2ab. Determination of Reference values of compressive strength and pore structure based on a Concrete according to 2a; 2 B. Definition of a minimum water film thickness in the range of 0.001 μm and 0.3 μm; 2c. determination Reference values for compressive strength and pore structure from a concrete according to 2b; 3. Setting up a Function based on the values of 2ab. and 2. 4. Implementation of steps 2 to 3 for any desired reduced Cement content. Method according to claim 1, characterized in that that the inert fines are at least 4.3 times as fine as the Cement. Method according to claim 1, characterized in that that the cement fine fines are up to twice as large like the cement.