Admixtures for Self-Consolidating Concrete

October 4th, 2020
5 min read

Self-consolidating concrete (SCC) is a highly flowable non-segregating mixture that can be placed under its own weight, i.e. with little or no vibration. The need for SCC has grown over recent years to meet designers’ specifications for more heavily reinforced concrete elements and more complex formworks. The SCC technology offers the following advantages:

  1. Faster casting rates with no mechanical vibration and less screeding.
  2. Improved and more uniform architectural smooth surface finishes, with little to no surface remedial works required.
  3. Ease of filling sections congested with reinforcements, hard-to-reach areas, and complex shapes, with little or no vibration.
  4. Opportunities to create structural and architectural shapes and surface-finishes not otherwise achievable with conventional concrete.
  5. Improved pumpability and uniformity of in-place concrete achieved by eliminating variable operator-related efforts of consolidation.
  6. Labor savings, shorter construction periods, and resulting overall cost savings.
  7. Reduction or elimination of vibrator noise, which may potentially lead to an increase in construction hours in urban areas.
  8. Minimized movement of ready-mixed trucks and pumps during placement, thus enabling the producer to service the project more efficiently.

Requirements for mix proportions

High deformability, high passing ability, and adequate resistance to segregation are required to achieve successful placement and performance of SCC.

The assessment of free or non-restricted deformability involves the evaluation of the capacity to deform, indicating how far the concrete can spread into the formwork, as well as the rate of deformability. When using the slump flow test, the deformation capacity refers to the final spread diameter, regardless of the flow velocity. Concrete that achieves high deformation capacity (or relatively low yield value) but spreads slowly (i.e. at moderate viscosity levels) may require some mechanical consolidation to ensure complete filling of the formwork. In order to secure good deformability, it is important to reduce the friction among solid particles. Aggregate inter-particle contact can decrease by reducing the aggregate content and increasing the paste volume required to maintain high passing ability among closely spaced obstacles. For the powder materials, the increase of inter-particle distance through an increase in water content can lead to segregation. A high-range water-reducing (HRWR) admixture is used to maintain a relatively low water-to-cementitious based materials ratio and reduce internal friction of solid particles.

The required level of passing ability is a function of structural detailing and formwork shape. SCC with high deformability but insufficient cohesiveness may not achieve complete passing ability to spread fully among closely spaced obstacles. Low cohesiveness can promote segregation and blockage. The blockage mechanism partly results from the collision and instantaneous contact among aggregate particles at the vicinity of an opening. Therefore, a lack of cohesiveness can lead to local aggregate separation and segregation that can block the flow of the concrete across obstacles. Passing ability can be compromised when the nominal aggregate size is large or the content of the coarse aggregate is high. Nevertheless, it should be mentioned that the segregation between aggregates and the cement paste, especially in the vicinity of reinforcements, could accentuate the risk of blockage as it leads to local increases in the concentration of large solid particles.

The third criterion for producing SCC is to provide high resistance to segregation after casting to ensure homogenous distribution of the in-situ quality of the hardened concrete. Adequate cohesiveness can be secured by incorporating a viscosity-modifying admixture (VMA), along with HRWR, to control bleeding, segregation, and surface settlement. Another way to enhance the cohesiveness of SCC is to reduce the free water content and/or increase the volume of fines and cement paste. Fine materials, such as supplementary cementitious materials and fillers of high surface area can adsorb greater content of water compared to cement particles and can reduce the free water content. Incorporating a VMA, which increases the capacity to retain free water and the viscosity of the suspended liquid phase, can control segregation between water and solid phases. Other categories of segregation, namely blocking and non- uniformity, can be reduced by having a paste phase capable of ensuring better suspension of solid particles in fresh concrete.

Holderchem SCC range of products

Holderchem offers a comprehensive range of high-range water reducing (HRWR) products and viscosity modifying agents to achieve SCC performance with superior flowability and rheology. Mix design property values vary depending on the ambient mix conditions and the quality of materials used. For indication purposes, we provide herein below a typical starting mix design formulation with indicative concrete properties:

MaterialDosage, kg/m3
Type I Portland cement450
Batimix Silica Fume 71036
Water-to-cementitious materials ratio0.42
Fine Aggregates815
Coarse Aggregates915
Batimix HWR 1500 (or HWR 1400)5.8 (or, 12.5)
Batimix VMA 5102.4

Concrete Properties
Air content2.5%
Slump flow600 to 725 mm
Setting time12 to 15 hrs
3-day compressive strength24 - 26 MPa
7-day compressive strength38 - 41 MPa
28-day compressive strength54 - 56 MPa

Specifications and Testing Methods

ACI 237R-07 Self-Consolidating Concrete specifications provides various known practices and processes for producing self-consolidating concrete.

To assess self-compacting properties, several standard tests have been used including the following:

  1. ASTM C1610, "Standard Test Method for Static Segregation of Self-Consolidating Concrete Using Column Technique," ASTM International, PO Box C700, West Conshohocken, PA, USA.
  2. ASTM C1611, "Standard Test Method for Slump Flow of Self-Consolidating Concrete," ASTM International, PO Box C700, West Conshohocken, PA, USA.
  3. ASTM C1621, "Standard Test Method for Passing Ability of Self-Consolidating Concrete by J-Ring," ASTM International, PO Box C700, West Conshohocken, PA, USA.
Related Products:

Batimix HWR 1400
BATIMIX HWR 1400 is a liquid high-range water-reducing (superplasticizer) admixture with enhanced properties for concrete. It is based on high-grade naphthalene sulfonate and carefully selected chemical materials.
Batimix HWR 1500
BATIMIX HWR 1500 is a high-performance liquid high-range water-reducing (superplasticizer) admixture for concrete. It is based on synthetic polycarboxylate acid derivatives and on carefully selected chemicals.
Batimix Silica Fume 710 D
BATIMIX Silica Fume 710 is a powder silica fume mineral additive used to produce high performance concrete. It is available in two forms: BATIMIX Silica Fume 710 U (i.e. Undensified), with bulk density typically 200 ~ 350 kg/m³ & BATIMIX Silica Fume 710 D (i.e. Densified), with bulk density typically 450 ~ 700 kg/m³.
Batimix Silica Fume 710 U
BATIMIX Silica Fume 710 is a powder silica fume mineral additive. It is used to produce high-performance concrete. It is available in two forms: BATIMIX Silica Fume 710 U, in an un-densified form with bulk density typically of 200 to 350 kg/m³, and BATIMIX Silica Fume 710 D, in a densified form with a bulk density of typically 450 to 700 kg/m³.
Batimix VMA 510
BATIMIX VMA 510 is a ready-to-use liquid admixture designed to modify the viscosity of fresh concrete. When used in conjunction with superplasticizer agents, highly flowable and self-consolidating concrete mixes can be successfully produced without bleeding or segregation.

Statement of Responsibility: The information and application advice contained in this document are based on the present state of scientific and practical knowledge of Holderchem SAL. It is provided with no warranty, implied or otherwise, as to its completeness or accuracy. Since methods and conditions of application and use are beyond the control of Holderchem, HOLDERCHEM MAKES NO WARRANTIES, IMPLIED OR OTHERWISE, AS TO THE MERCHANTABILITY OR FITNESS FOR ORDINARY OR PARTICULAR PURPOSES OF ITS PRODUCTS AND EXCLUDES THE SAME. Holderchem warrants that its products shall be of sound materials and workmanship. As products are applied, handled and stored in manners and site conditions over which Holderchem has no control, Holderchem’s liability in respect of any material which can be proven defective shall be limited to the replacement of such defective material or reimbursement of its cost at Holderchem’s option. Holderchem shall not be liable for any consequential or incidental damage or loss arising out of the use of its products.

Important Note: Holderchem shall have the right to modify product specification sheets at any time without previous notice. Buyers should always refer to the most recent data sheets, copies of which can be supplied upon request. The sale of products mentioned in this literature shall be subject to Holderchem’s General Conditions of Sale Delivery and Payment[Visit: https://holderchem.net/gcsdp]

Holderchem R&D
Holderchem R&D seeks to develop solutions to meet construction challenges by bringing to market innovative products and systems, which offer benefits across the complete life cycle of buildings and other constructions. The aim is to supply customers with high-performance products to help them achieve better productivity, lower overall costs, and achieve extended service life and functionality. Research also aims at developing the Holderchem range of Batimix products with a particular focus on polymer emulsions, polymer-inorganic interactions, and product applications.
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