AU2021101949A4 - A Kind of Green High Performance Concrete - Google Patents

Abstract

The invention discloses a kind of green high performance concrete (HPC), belonging to the technical field of building materials. The ultra-high performance concrete (UHPC) in the present invention comprises the following raw materials in percentage by weight: 33-35% of cement, 12-15% of steel slag powder, 3-5% of composite expansive agent, 18-20% of micro nano active admixture, 8-10% of silica fume, 18-20% of quartz sand, 1.6-1.8% of waterreducer and 1.8-2% of steel fiber. Specifically, the micro-nano active admixture is a mixture of silicon rich iron tailings, slag, fly ash and quartz powder in a mass ratio of 44:22:28:6. The UHPC of the invention has good working performance, wherein, under standard curing conditions, the flexural strength can reach 25.6MPa, compressive strength can reach 142MPa, and elastic modulus can reach 52.4GPa, respectively. Besides, the adiabatic temperature rise is only 59.7 C and the drying shrinkage rate in 180d is only 280x106.

Description

A Kind of Green High Performance Concrete

TECHNICAL FIELD

The invention relates to the technical field of building materials, in particular to a green

high performance concrete.

BACKGROUND

Ultra-high performance concrete (UHPC), different from traditional high-strength

concrete (HSC) and steel fiber reinforced concrete (SFRC), refers to a new type of

cement-based engineering material whose properties, such as mechanical properties,

durability and so on, are far superior to ordinary concrete and high performance concrete.

Further, it is also called reactive powder concrete (RPC), because its preparation method

can increase the fineness of raw materials and improve the active components

(pozzolanic activity).

As a modern advanced material, on one hand, UHPC innovates the composite mode of

cement-based materials (concrete or mortar), fiber and steel (steel bar or high-strength

prestressed steel bar); on the other hand, it greatly raises the strength utilization efficiency

of fiber and steel bar in concrete. Therefore, great progress has taken place in the

comprehensive performance of cement-based structural materials. In terms of its

excellent mechanical properties and durability, UHPC has been paid much attention since

it came out, and the research on UHPC is becoming increasingly mature. Specifically,

researchers have done a lot of research work on raw material composition, mix design,

mechanical properties, durability, working performance and microstructure of UHPC.

In recent years, with the technical development of superplasticizer and superfine mineral

admixture, UHPC with 100-150 MPa can be prepared through conventional materials and

general technology. Moreover, UHPC is gradually replacing ordinary concrete in some

practical projects because of its ultra-high strength, ultra-high toughness, ultra-low wear

coefficient and high environmental protection property. For example, UHPC has been

used in structures with thin structural dimensions, such as steel bridge deck pavement and

prefabricated part.

However, for some mass concrete structures requiring ultra-high performance, the

application of UHPC in similar projects is limited because of the high hydration heat and

shrinkage caused by the large amount of cement in the preparation process. Therefore, it

is an urgent technical problem to provide UHPC with low heat of hydration and low

shrinkage.

SUMMARY

The purpose of the present invention is to provide a green high-performance concrete to

solve the problems existing in the prior art, so that the UHPC can be equipped with low

hydration heat and low shrinkage.

To achieve the above-mentioned purpose, the present invention provides the following

scheme.

A kind of UHPC is proposed by the invention, which consists of the following raw

materials in percentage by weight.

33-35% of cement, 12-15% of steel slag powder, 3-5% of composite expansive agent, 18

% of micro-nano active admixture, 8-10% of silica fume, 18-20% of quartz sand, 1.6

1.8% of water reducer and 1.8-2% of steel fiber. Wherein, the micro-nano active admixture is a mixture of silicon-rich iron tailings, slag, fly ash and quartz powder with a mass ratio of 44:22:28:6; the specific surface area of the micro-nano active admixture is more than 1000 m2 /kg.

The composite expansive agent is magnesium composite expansive agent.

Further, the cement is Huaxin P- 42.5 grade cement.

Further, the quartz sand is in 20-200 meshes and contains 99.6% SiO2.

Further, the silicon content in the silica fume is more than 98%.

Further, the specific surface area of the steel slag powder is 600m 2 /kg.

Further, the steel fiber is copper-plated steel fiber with a diameter of 0.22 mm.

Further, the water reducer is polycarboxylic acid water reducer CP-J.

Furthermore, the water to binder ratio of the UHPC is 0.16, and the binder to sand ratio is

1:1.

The invention discloses the following technical effects.

(1) In the present invention, the ratio of water to binder is 0.16, of binder to sand is 1:1, of

cement to steel slag powder to expansive agent to micro-nano material to silica fume is

:15:5:20:10, and the amount of admixture- quartz powder is adjusted appropriately, so

that the prepared UHPC has good working performance, specifically, under standard

curing conditions, the flexural strength can reach 25.6MPa, compressive strength can

reach 142MPa, and elastic modulus can reach 52.4GPa, respectively. Besides, the

adiabatic temperature rise is only 59.7C and the drying shrinkage rate in 180d is only

280x10-6.

(2) The compressive strength of UHPC has a good correlation with the compactness of

cementitious material system, that is, the strength of UHPC increases with the decrease of porosity of cementitious material. In addition, the addition of mineral admixtures can not only adjust the particle size distribution of cementitious materials to realize dense filling, but also give full play to the pozzolanic effect to improve the strength of UHPC.

Moreover, the hydration heat of UHPC can be obviously reduced by adding a large

amount of mineral admixture and quartz powder.

(3) The addition of steel slag powder can not only effectively reduce the hydration heat of

UHPC, but also inhibit the shrinkage. Besides, the drying shrinkage of UHPC can be

greatly reduced by adding a small amount of ettringite composite expansive agent.

(4) The hydrated products in UHPC mainly consist of dense and heterogeneous hydrated

calcium silicate. Further, a small amount of ultrafine quartz powder particles can react in

alkaline environment to form a continuous and dense transition zone with hydrated

calcium silicate gel, which improves the interface structure between aggregate and

hydrated products.

BRIEF DESCRIPTION OF THE FIGURES

In order to explain the embodiments of the present invention or the technical scheme in

the prior art more clearly, the figures needed in the embodiments will be briefly

introduced below. Obviously, the figures in the following description are only some

embodiments of the present invention, and for ordinary technicians in the field, others can

be obtained according to these figures without paying creative labour.

Figure 1 shows the change of porosity of admixture compact.

Figure 2 indicates the influence of quartz powder content on the porosity of aggregate

system.

Figure 3 is an adiabatic temperature rise diagram of UHPC with low hydration heat and

low shrinkage.

Figure 4 is a dry shrinkage diagram of UHPC with low hydration heat and low shrinkage.

Figure 5 is a typical SEM micrography of UHPC with low hydration heat and low

shrinkage. Wherein, (a) is a gel structure and (b) is a binder-bone interface structure.

DESCRIPTION OF THE INVENTION

Various exemplary embodiments of the present invention will now be described in detail,

which should not be regarded as a limitation of the present invention, but rather as a more

detailed description of certain aspects, characteristics and embodiments of the present

invention.

It should be understood that the terms described in the present invention are only for

describing specific embodiments and are not intended to limit the present invention. In

addition, as for the numerical range in the present invention, it should be understood that

every intermediate value between the upper limit and the lower limit of the range is also

specifically disclosed. Intermediate values within any stated value or stated range and

every smaller range between any other stated value or intermediate values within the

stated range are also included in the present invention. The upper and lower limits of

these smaller ranges can be independently included or excluded from the range.

Unless otherwise stated, all technical and scientific terms used herein have the same

meanings as commonly understood by those skilled in the art to which the present

invention relates. Although the present invention only describes preferred methods and

materials, any methods and materials similar or equivalent to those described herein may

be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe methods and/or materials related to the documents. In case of conflict with any incorporated documents, the contents of this specification shall prevail.

Without departing from the scope or spirit of the invention, it is obvious to those skilled

in the art that many modifications and changes can be made to the specific embodiments

of the specification of the invention. Other embodiments derived from the description of

the present invention will be apparent to the skilled person. The specification and

examples of this application are only exemplary.

As used herein, "including", "comprising", "having", "containing" and so on, are all open

terms, which means including but not limited to.

Unless otherwise specified, "parts" mentioned in the present invention are calculated by

mass parts.

The micro-nano active admixture (ICBM) of the invention takes slag (S), steel slag (I),

fly ash (C) and quartz powder (Q) as raw materials. Preferably, it is a mixture of silicon

rich iron tailings, slag, fly ash and quartz powder according to the mass ratio of

44:22:28:6, further, the specific surface area of the micro-nano active admixture is larger

than 1000 m2 .

The water reducer used in the invention is polycarboxylic acid water reducer CP-J.

The main physical performance indexes of cement, silica fume, steel slag powder and

micro-nano materials used in the invention are shown in Table 1.

Table 1 Raw Density Specific Water Mobility R28P 28d compressive material /g -cm area/m2-kg-c ratio/% ratio/% strength ratio/% Cement 4.20 380 100 100 49.3 100.0 Silica fume 2.30 / 115 90 52.1 105.7

Steel slag 2.81 600 105 100 40.7 82.6 powder Micro nano 2.64 1200 95 110 42.5 86.2 materials The particle size distribution of cement and mineral admixture is shown in Table 2.

Table 2 No. D50/[m D10/ m D25/[m D75/[m D90/tm P-0 42.5 14.50 2.54 5.58 20.24 36.74 cement Silica fume 0.50 0.14 0.25 0.86 1.02 Steel slag 14.10 2.12 5.08 20.02 35.25 powder Micro-nano 1.00 0.61 0.78 1.42 1.99 materials 1. Study on porosity of UHPC cementitious materials and aggregate systems with

different compositions

Adjusting the proportion of particles with different sizes in the cementitious material

system will cause the change of porosity. Based on the particle dense packing theory, the

composite cement dry powder compact is prepared by mechanical pressure method, and

the dense packing of particles with different sizes is studied by testing the porosity of the

compact. It can be seen from Table 2 that the cement and steel slag powder of D50 are

14.50tm and 14.10tm, respectively. Since their fineness is similar, the invention

considers that the proportion change has little effect on the bulk density of the

cementitious material system. Taking the ternary system of cement-micro-nano-silica

fume as basis, the influence of different particle sizes on the compactness of adhesive

material is studied. Fig.1 shows the porosity changes of cement, micro-nano and silica

fume compacts with different proportions, in which the proportions of micro-nano and

silica fume are respectively 3:1, 2:1, 1:1, 1:2 and 1:3, and the total proportion of

admixture is respectively 20%, 25%, 30%, 35% and 40%. It can be seen from the figure that the porosity of the adhesive system is reduced to varying degrees by the addition of different amounts of micro-nano and silica fume, further, the overall porosity decreases first and then increases with the increase of the content of micro-nano and silica fume.

When the ratio of cementitious materials compact cement, micro-nano materials and

silica fume is 70:20:10, the lowest porosity of the system is only 34.0%, followed by

34.2% with ratio of 80:5:15. At this time, it is considered that silica fume and micro-nano

can fully fill the larger cement particles, and play their dense filling role, thus improving

the bulk density of ternary cementitious system, which is basically consistent with the

maximum density theory. However, with the further increase of the content of micro

nano and silica fume, the accumulation of large cement particles will be affected due to

the effect of wall attachment, which will reduce the compactness and increase the

porosity of the whole system.

The proportion of particles with different sizes in aggregate system directly affects the

continuity of aggregate and the compactness of the system. In this invention, continuous

graded quartz sand of 20-120 meshes and quartz powder of 200 meshes are used to

prepare aggregate. Fig.2 shows the influence of different quartz powder content on the

porosity of aggregate system. It can be seen that with the increase of 200-mesh quartz

powder content, the porosity of aggregate system first decreases rapidly and then

increases. When the content of quartz powder reaches 15%, the porosity of the whole

aggregate system is the lowest and the bulk density is the highest.

2. Mix design of UHPC

On the basis of a large number of preliminary exploratory tests, the mix proportion of

UHPC is designed combined with the results of dense packing test. The cementitious material and aggregate are prepared by three combinations with the lowest porosity of cementitious material system and aggregate system respectively, shown in Table 3. It can be seen from the test results in Table 3 that the compressive strength of UHPC has a good correlation with the compactness of the cementitious material system. Specifically, with the decrease of the porosity of the cementitious material, the ternary cementitious material tends to be more closely packed, and the compressive strength of UHPC also increases, which indicates that the stacking mode of cementitious material particles has a great influence on the macro-mechanical properties of UHPC. In other words, the closer the particles with different sizes are stacked, the smaller the porosity is, and theoretically, the matrix can obtain higher mechanical strength. When the ratio of cement, micro-nano and silica fume is 70:20:10, the compressive strength of each specimen reaches the highest in the same group, which is consistent with the experimental results of Fig.1. In addition, it is found that with the increase of silica fume content and the decrease of ultrafine powder content, the working performance of UHPC decreases gradually. When the ratio of cement, micro-nano and silica fume is 80:5:15, the expansion degree of

UHPC decreases by 50mm, which is mainly because the self-made ultrafine powder

adopts physical viscosity reduction technology, which has obvious ball effect and certain

physical water reduction effect.

The test results in Table 3 show that the particle stacking morphology of aggregate has

great influence on the mechanical properties and working properties of UHPC. In the

same cementitious material system, the fluidity of UHPC mixture decreases with the

increase of quartz powder content, which is mainly due to the large specific surface area

of quartz powder and the increase of water demand. Therefore, water-binder ratio 0.16, binder-sand ratio 1:1, cementitious materials ratio 70:20:10, quartz powder content 20%, water reducer content 1.8% and steel fiber volume content 2% are selected as the optimized basic ratio.

Table 3 Cement: Steel 28d Water- Binder- micro- Quartz Water fiber Expansion compressive No. binder sand nano powder reducer volume degree strength ratio ratio materials: content content content /mm/MPa silica fume 1 0.16 1:1 70:20:10 15 1.8 2 635 148.2 2 0.16 1:1 70:15:15 15 1.8 2 610 140.5 3 0.16 1:1 80:5:15 15 1.8 2 585 143.8 4 0.16 1:1 70:20:10 20 1.8 2 610 152.3 0.16 1:1 70:15:15 20 1.8 2 595 143.4 6 0.16 1:1 80:5:15 20 1.8 2 575 145.6 7 0.16 1:1 70:20:10 25 1.8 2 590 146.5 8 0.16 1:1 70:15:15 25 1.8 2 565 133.8

9 0.16 1:1 80:5:15 25 1.8 2 560 139.0 3. Preparation of UHPC with low hydration heat and low shrinkage

It can be seen from the basic ratio that UHPC has a very large proportion of cement,

which will inevitably lead to high hydration heat and large shrinkage of UHPC. When

preparing high-strength concrete, people usually add a large amount of mineral admixture

to reduce hydration heat and shrinkage. Steel slag powder is a mineral admixture made by

grinding steel-making industrial waste residue, which contains a certain amount of

clinker minerals such as C2S and C3S, as well as a large amount of CaO and MgO, which

not only has high potential activity but also contributes to inhibiting shrinkage. Therefore,

ultra-fine steel slag powder is used as mineral admixture, and a certain amount of

expansion agent is used to prepare UHPC with low hydration heat and low shrinkage. On the basis of optimized ratio, steel slag powder and composite expansion agent are used to directly replace cement for testing. The test ratio and results are shown in Table 4

. Table 4

Content of Content of Expansion 28d Adiabatic 180d dry No. steel slag expansive degree compressive temperature shrinkage powder agent /mm strength /MPa rise/°C /10-6 1 0 0 610 152.3 65.6 480 2 10 0 610 144.5 62.8 446 3 15 0 605 142.6 60.6 428 4 20 0 600 132.6 57.3 408 0 5 590 146.3 63.5 336 6 15 5 585 141.8 59.5 285

7 15 8 560 134.5 57.2 268 It can be seen from Table 4 that with the increase of steel slag powder content, the

expansion degree of UHPC changes little and the compressive strength decreases

gradually, but when the content is less than 15%, the strength decreases little, and when it

exceeds 15%, the strength will decrease greatly. The addition of steel slag powder can

reduce the adiabatic temperature rise and dry shrinkage of UHPC, especially the adiabatic

temperature rise. This is because when preparing UHPC, the water-binder ratio is low,

and some cement particles can't be hydrated, but can only play a filling role. After ultra

fine grinding, the potential activity of steel slag powder is excited so that it can replace

some cement and give full play to its activity and filling role. Therefore, the cement

consumption is reduced causing reduced hydration heat. Moreover, the components such

as CaO and MgO contained in UHPC can also inhibit the drying shrinkage of UHPC to

some extent. The addition of composite expansion agent can obviously inhibit the drying

shrinkage of UHPC, and the drying shrinkage rate gradually decreases with the increase

of expansion agent content. However, when the recommended amount of expansion agent is 8%, the fluidity and compressive strength of UHPC decrease obviously. Considering the workability, compressive strength, adiabatic temperature rise and dry shrinkage of

UHPC, it is advisable to select 15% of steel slag powder and 5% of expansive agent.

Compared with the basic ratio, the adiabatic temperature rise decreases by 6.1°C, and the

dry shrinkage rate decreases by 195x106 in 180d days.

4. Performance test of low hydration heat and low shrinkage UHPC.

Test method:

(1) The working performance test shall be conducted in accordance with Standardfortest

method of mechanicalpropertieson ordinaryconcrete (GB/T 50081-2002).

(2) The mechanical property test shall be conducted in accordance with Standardfor test

methods of mechanicalpropertieson ordinary concrete (GB/T 50081-2002) and Reactive

powder concrete (GBT31387-2015), wherein, the concrete specimen shall be a cube

specimen with the size of 100mm.

(3) Shrinkage and durability tests shall be conducted in accordance with Standardfortest

methods of long-term performance and durability of ordinary concrete (GB/T 50082

2009).

According to the above test results, the final test ratio is determined and the performance

test is carried out. Ratio and test results are shown in Table 5. From the data in the table,

it can be seen that UHPC has good working performance, with 28d flexural strength and

compressive strength reaching 25.6MPa and 142.OMPa respectively, elastic modulus

exceeding 50GPa, adiabatic temperature rise below 60°C and dry shrinkage rate below

300x10-6. Test results of adiabatic temperature rise and dry shrinkage performance are

shown in fig.3 and fig.4. It can be seen from fig.3 that the adiabatic temperature rise peak of UHPC material with low hydration heat and low shrinkage appears at 89.7C within

31.5h after entering the mold, and the time of appearing temperature peak is obviously

longer than that of ordinary concrete. This is because the special retarding

polycarboxylate water reducer can effectively delay the early hydration heat release rate

of cement and play a positive role in reducing the adiabatic temperature rise of concrete.

It can be seen from fig.4 that the dry shrinkage rate of UHPC increases greatly within 60

days, and gradually stabilizes after reaching 120 days, and the dry shrinkage rate after

180 days is only 280x10-6, which is significantly lower than that of ordinary C50

concrete, which should be attributed to 50% composite mineral admixture and expansive

agent, which effectively inhibits the shrinkage of UHPC.

Table 5

Cement: steel Water- Binder- slag powder: Quartz Water Steel mx binder sand expansive agent: Mix bid r ad micro-nano powder reducer fiber proportion ratio ratio material: silica fume 0.16 1:1 50:15:5:20:10 20 1.8 2 28d Elastic Adiabatic 180d Fluidity flexural 28d compressive modulus temperature drying Performance /mm strength strength /MPa /GPa rise /C shrinkage test /MPa rate /106 590 25.6 142.0 52.4 59.7 280 5. Microanalysis of UHPC under standard curing

Fig.5 is a typical SEM micrography of UHPC with low hydration heat and low shrinkage

for 28 days under standard curing conditions. It can be seen from (a) and (b) that the hydration products of UHPC are mainly dense and heterogeneous hydrated calcium silicate, mixed with many mineral admixtures with partially hydrated or un-hydrated surface, and it is difficult to find needle-like or flaky calcium hydroxide crystals. The results show that the large amount of steel slag powder, ultrafine powder and silica fume can not only fill the dense cementitious material system well, but also give full play to the pozzolanic activity of the three materials, and consume a lot of calcium hydroxide produced by cement hydration, thus making UHPC system more dense. From (b), it can be clearly observed that there are two types of interface bonding between cementitious materials and quartz sand aggregates. One is that the interface between hydrated calcium silicate gel and large grain quartz sand is clear, and there is no obvious interface transition zone, but the bonding is quite tight; the other is that the interface between a small amount of ultrafine quartz powder particles and hydrated calcium silicate gel is unclear, and there is a continuous and dense transition zone, which indicates that the surface of some ultrafine quartz powder particles reacts and forms a compact whole with hydration products, further improving the interface structure as well as the compressive strength of UHPC.

The above embodiments only describe the preferred mode of the invention, but do not

limit the scope of the invention. On the premise of not departing from the design spirit of

the invention, various modifications and improvements made by ordinary technicians in

the field to the technical scheme of the invention shall fall within the protection scope

determined by the claims of the invention.

Claims (8)

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. The UHPC is characterized by comprising the following raw materials in percentage

by weight.

33-35% of cement, 12-15% of steel slag powder, 3-5% of composite expansive agent, 18

% of micro-nano active admixture, 8-10% of silica fume, 18-20% of quartz sand, 1.6

1.8% of water reducer and 1.8-2% of steel fiber. Wherein, the micro-nano active

admixture is a mixture of silicon-rich iron tailings, slag, fly ash and quartz powder with a

mass ratio of 44:22:28:6; the specific surface area of the micro-nano active admixture is

more than 1000 m2 /kg.

The composite expansive agent is magnesium composite expansive agent.

2. The UHPC according to claim 1, characterized in that the cement is Huaxin P-0 42.5

grade cement.

3. The UHPC according to claim 1, characterized in that the quartz sand is in 20-200

meshes and contains 99.6% SiO2.

4. The UHPC according to claim 1, characterized in that the silicon content in the silica

fume is more than 98%.

5. The UHPC according to claim 1, characterized in that the specific surface area of the

steel slag powder is 600 m 2 /kg.

6. The UHPC according to claim 1, characterized in that the steel fiber is copper-plated

steel fiber with a diameter of 0.22 mm.

7. The UHPC according to claim 1, characterized in that the water reducer is

polycarboxylic acid water reducer CP-J.

8. The UHPC according to claim 1, characterized in that the water to binder ratio of the

UHPC is 0.16, and the binder to sand ratio is 1:1.