MICRO CONCRETE

MICRO CONCRETE

Micro-concrete is generally used as a repair material which is of non shrinking type. The application areas include:

Repair of damaged reinforced concrete elements like beams, columns, wall, etc. where access is restricted and compaction is not possible. 
For jacketing of RCC columns to increase load-taking capacity (strengthening of a vertical members)
Microconcrete is combination of cement, high quality graded fine aggregate, shrinkage compensating agents and dispersion agents in powder form marketed as dry powder in packets by construction chemical companies. This is to be mixed with predetermined amount of water depending on the consistency sought – trowelable or pourable. Applied as repair mortar or to fill the crevices which cannot be done by conventional concrete.

Micro concrete is a dry ready mix cementitious based composition formulated mainly for used in repairs works when the concrete is damaged and the area is restricted in movement due to which there is problem in placing concrete. Micro concrete is in dry powder from added with clean water on the site and its a good quality cement.

Renderoc constructive solutions ® RG Spl 

General purpose, non-shrink, cementitious micro-concrete

Uses

 Renderoc RG Spl is used for repairs to damaged reinforced concrete elements, particularly where access is restricted and where vibration of the placed material is diffi cult or impossible.

 It is suitable for various structural strengthening measures such as encasement build-ups, jacketing , piletop encapsulation resin system, etc. 

Advantages

  Gaseous expansion system compensates for shrinkage and settlement in the plastic state. 

 Can be pumped or poured into restricted locations. 

 Fluidity to allow for placement without vibration.

  Pre-bagged to overcome site-batched variations.

  Rapid strength gain to facilitate early reinstatement.

  High ultimate strengths and low permeability of cured repair.

  Contains no chloride admixture. 

 Ensures piletop integrity as part of a waterproofing system

Description 

Renderoc RG Spl is supplied as a ready to use blend of dry powders which requires only the site addition of clean water to produce a free-fl owing non-shrink repair micro concrete. The material is based on Portland cements, graded aggregates and fillers, and additives which impart controlled expansion characteristics in the plastic state, while minimising water demand. The low water requirement ensures high early strength and long-term durability.

 For larger repairs, the mixed Renderoc RG Spl may be modified by the addition of 5mm to 12mm clean, graded, saturated surface dry aggregates at site.

Design criteria

 Renderoc RG Spl can be applied in sections upto 100mm deep. For larger sections, the addition of approved aggregates may be required. This will depend on the specific configuration of the repair location. 

Properties 

The following results were obtained at a water:Powder ratio of 0.15 @ 300C. 

Test                                Typical result at 300C

 Compressive strength (N/mm2 )

 1 Day                                    30

 7 Days                                  60 

28 Days                                 75

 Flexural strength                   8N/mm2 @ 28 days 

Young’s Modulus                    25 kN/mm2

 Thermal conductivity             1.5 W/m0C 

 Fresh wet density                  2300 - 2400 kg/m3 

 Specification clauses

 Performance specification

 The fluid micro-concrete repair material shall be Renderoc RG Spl, a single component, cement based, micro-concrete to which only the site-addition of clean water ( and approved graded coarse aggregates where specified) shall be permitted. The micro-concrete shall contain no metallic aggregates, or chlorides and shall be shrinkage compensated in the plastic state. The micro concrete in the flowable consistency should achieve a compressive strength of not less than 30N/mm2 after 24 hours at 300C. Most importantly, the cured microconcrete shall have a coeffi cient of thermal expansion similar to that of the host concrete.

Application instructions

Preparation 

The unrestrained surface area of the repair must be kept to a minimum. The formwork should include drainage outlets for pre-soaking and, if beneath a soffi t, provision for airventing. Provision must also be made for suitable access points to pour or pump the mixed micro-concrete in place

Defective concrete surfaces must be cut back to a sound base. Smooth surfaces should be mechanically roughened. Corroded reinforcing steel should be exposed around its full circumference and cleaned to remove all loose scale and corrosion deposits. It is important to clean the steel to a bright condition. Grit-blasting is recommended. One coat of Nitozinc Primer should be applied on the reinforcing steel. If any discontinuity in the applied fi lm is noticed, one more coat has to be applied. Several hours prior to placing, the concrete substrates should be saturated with clean water. Immediately prior to placing, any free water should be removed. 

Mixing 

Care should be taken to ensure that Renderoc RG Spl is thoroughly mixed in a forced-action mixer of adequate capacity. Alternatively, mix in a suitably sized drum with a high torque (400/500 rpm) rotary drill fitted with a mixing paddle. It is essential that machine mixing capacity and labour availability is adequate to enable the placing operation to be carried out continuously. The quantity water required will generally be between 3.50 litres and 3.75 litres per 25 kg bag of Renderoc RG Spl. The optimum water content should be determined and accurately measured into the mixer. However it should not exceed 3.75 litres/25 kg in any case. With the mixer running, slowly empty Renderoc RG Spl bag into the mixer. Mix continuously for 5 minutes, ensuring a smooth even consistency of the mix. Where the addition of graded coarse aggregate has been specified it should be added after the water and Renderoc RG Spl are properly mixed. Mixing should then continue for a further 1 minute to ensure proper dispersion.

Form Work 

Slurry tight form work that will not deform or leak when subjected to hydraulic pressure imposed by the micro concrete will be fabricated and erected where the material is gravity fed, provision in the formwork will be made for a suitable feedhopper at the highest point. Where necessary, provision will be made for airvents to prevent air entrapment. Form work will be coated with Reebol mould releasing agent prior to fixing.

Placing 

The mixed material should be placed immediately. if placed by pump, standard concrete pumping practice should be followed. The pump and pipeline must be primed with cement slurry. Pumping should be commenced immediately after priming. If poured in the form work, avoid air entrapment by pouring from one side only. 

Curing 

As Renderoc RG Spl is a cement-based repair material, it should be cured immediately after stripping the formwork in accordance with good concrete practice. the use of Nitobond AR or any of Fosroc’s Concure range of curing compounds, sprayed on the surface of the Renderoc RG Spl. in a continuation fi lm, is recommended soon after tripping the form work. In harsh drying conditions, supplementary curing such a wed hessian or/or polythene sheeting must be used. 

 .

EPC

Expanded Polystyrene Concrete

Abstract

EPS concrete was produced by mixing the expanded polystyrene spheres (EPS) and polymer emulsion and thickener to the matrix concrete, and this concrete had good vibration energy absorption characteristics. Based on the experimental data obtained on EPS volume ratio of 0%, 20%, 30%, and 40% by replacing matrix or coarse aggregate, the two design styles had nearly the same compressive strength. By applying frequency of 5 Hz, 50000 or 100000 times, 40 KN, 50 KN, and 60 KN cyclic loading, it is shown that the higher the inclusion size was, the lower the compressive strength of the EPS concrete would be; the larger the applying dynamic cyclic load was, the more obvious the compressive strength changing would be. Meanwhile, the strength of EPS concrete had no evident change after durability test. The results of this research had practical significance on using EPS concrete in some long-term cyclic dynamic load engineering.

1. Introduction

Because the expanded polystyrene (EPS) light weight concrete has the characteristics of lightweight, energy absorption, and heat preservation, it is used in many specific construction industries like high rise buildings, floating marine platforms, and large-sized and long-span concrete [1, 2]. The lightweight concrete (LWC) has no pollution to the environment because manufacture EPS particle consumes little energy, and the particle has no poison and harm. The EPS concrete has the characteristics of economy, environmental protection, and energy saving, meeting the design concept of modern construction material.

 2. Materials and Mix Design Principles

The test specimens were made with the same type as that used for very high strength concrete, and the EPS particle took the place of part of the concrete or coarse aggregate.

(1) Cement. It was made with CEM I 52.5 cement.

(2) Fine Aggregate. It is made with rounded river sand with a fineness modulus of 2.85.

(3) Coarse Aggregate. It is gravel with a diameter range of 4–20 mm.

(4) EPS Particles. EPS particles are expanded polystyrene spheres particle with a diameter range of 1–3 mm and density of 20 kg/m3 which is shown in Figure.

 (5) Silica Fume. Because the fineness of silica fume is very low, it is about 80–100 compared to normal cement and it is used in the concrete to fill up the pore among the cement granules and the hydrate products are similar to cement in water; the other mixture would been bonded by the gel.

 (6) Admixture. A polycarboxylate-based superplasticizer was used to improve the workability and the compressive strength of the EPS concrete. Expanded polystyrene spheres particles are hydrophobic material, extremely light with the density of only 12–20 kg/m3 which can cause segregation in mixing and make the inhomogeneity of the EPS concrete, leading to the decrease of the compressive strength.

(7) Mixing Method. Because of the hydrophobic material of the EPS particles, the workability and durability of EPS concrete were poor during the mixing process. Indeed, after numerous mixing, a mixing method similar to the “sand-wrapping” technique was utilized to make EPS concrete. Firstly, it pulled the EPS particles and 1/3 water and 1/2 polymer emulsion into the mixed hopper. After mixing of one minute, it introduced the gravel into the mixed hopper and then mixed it for one minute and finally it pulled all the other aggregates into the mixed hopper and mixed them for two minutes. The mixing method would ensure the workability and homogeneousness of the EPS concrete.

3. Compressive Strength Test

Cubes of 100 mm size of EPS concrete were used for studying the compressive strength after being stored in laboratory conditions for 28 days. Water-cement ratio is an important index to influence the compressive strength. The compressive strength significantly reduces as the water-cement ratio is set to 0.36, because the EPS particles are of hydrophobic material and the workability falls when the water-cement ratio increases. The compressive strength changes slightly when the water-cement ratio increases from 0.32 to 0.34, considering the economics as it applied to practical engineering the water-cement ratio is set to 0.32 in this paper.

 Failure Mode. Different ratio of the EPS particles volume had different failure mode which is shown in Figure. The matrix was fracture after the compressive strength test, and the scale of crack was smaller along with the increase of the EPS particles volume ratio. This phenomenon was caused by the characteristics of energy absorption of EPS particles, and the appearance was still intact even if the EPS concrete was under destruction.

4. The Durability of EPS Concrete

EPS concrete has the characteristics of vibration resistance and energy absorption, which can be used in civil construction based on cycle loading to reduce vibration of system. However, it has great significance to test the durability of EPS concrete with vibration property since vibration load infliction often goes with the characteristic of low durability. This paper qualitatively analyzes the influence of EPS volume ratio, vibration cyclic times, and vibration load on EPS concrete durability by cycle loading test.

Cyclic dynamic vibration test used a 370.50 MTS electrohydraulic servo fatigue test system shown in Figure which had 500 KN load capacity and 150 mm dynamic travel and test data could be real-time shown and stored in the computer. EPS volume ratio was 0%, 20%, 30%, and 40%, times of vibration cycle were 50000 and 100000, vibration load was 60 KN, 50 KN, and 40 KN, and vibration frequency was 5 Hz; the sine wave was adopted to simulate the vibration process.

5. Conclusions

EPS concrete has the advantages of small density, thermal insulation, and good seismic performance. So it is of great significance on the study of modern structural materials and practical engineering to research new concrete materials. The experimental investigations were conducted on three types of EPS concrete having EPS concrete of particles volume ratio ranging from 0% to 40%, with a view to confirming the presence of an intrinsic particle content effect on the EPS concrete compressive strength and durability.

 The conclusions are drawn as follows.

(1)In order to increase the compressive strength the polymer emulsion is mixing in the concrete grout which would bound other mixtures together, and the relationship between its mixing ratio and compressive strength is discussed. The hydroxypropyl cellulose is mixed in the EPS concrete for improving the workability of the grout and the influence of its mixing ratio on the concrete compressive strength is studied.

(2)The compressive strength of two types of EPS concrete in which concrete is replaced or only gravel replaced by EPS particles was basically identical; the result showed that the compressive strength of the two design styles was basically coinciding. The compressive strength of EPS concrete decreased obviously with the increase of EPS particles volume ratio; the reduction curve was similar to exponential type curve.

(3)The value of applying dynamic cyclic load had great effect on the compressive strength after durability test. The compressive strength of EPS concrete of particles volume ratio of 40% was increased after applying 40 KN and 50 KN cyclic dynamic load, and the other ratio of EPS particles volume concrete was reduced after durability test; meanwhile, the degree of compressive strength reduction was inversely proportional to EPS particles volume ratio. Also, the bigger the applying dynamic cyclic load was, the bigger the gap of compressive strength between before and after durability test would be. The compressive strength of EPS concrete of particles volume ratio of 0% and 30% would fall when dynamic cyclic load is applied 100000 times, and the reduction of matrix compressive strength was much more bigger than EPS concrete particles volume ratio of 30% compared with applying dynamic vibration load 50000 times.

(4)Through the results from the designed durability test, it proved that the EPS lightweight concrete has good durability and it has a very good use in practical engineering which has certain seismic requirements and applied cyclic load.

POLYSTYRENE BEAD IN CONCRETE

 

How to Add Polystyrene Beads to Concrete

 Polystyrene beads are a familiar item if you've ever owned a bean bag chair, but you probably didn't know you can create lightweight concrete by adding them to the mix. As a very light but strong building component EPS concrete, or expanded polystyrene concrete has highly insulating properties and can create a stone-like surface for creative projects. Garden statues, curved projects, panels of energy-efficient homes or unusual items such as concrete counter tops can be created using EPS concrete. Adding the polystyrene beads mainly requires knowing the ratio of the mix.

 

Step 1

Use a ratio of one to six for the mix of cement to polystyrene. Use equal parts Portland cement, sand and water. For example if you have 1 cup of Portland cement, mix it with 6 cups of polystyrene beads plus 1 cup water and 1 cup sand. This recipe is obviously very small but gives the correct ratio.

Step 2

Place the water in a large bucket such as an empty 5-gallon bucket, the concrete mixer or the wheelbarrow. The wheelbarrow can be cumbersome for mixing but if the batch is relatively small it should work. The bucket works for very small projects.

Step 3

Add the Portland cement and sand to the water and mix well to create a soup. This should be a very wet consistency, not usual for cement because the polystyrene will soak up a large amount of the water. Use the shovel to mix by hand or turn the cement mixer on if you have one.

Step 4

Place 1 part of the polystyrene beads in, allowing them to begin to be absorbed in the mix. Add 1 more portion, then another, until all of them are absorbed. Stop mixing as soon as the beads are mixed in. If the mix seems dry add a small amount of water so it comes to a less stiff consistency. The mix should be somewhat thick and not soupy, and what is called low-slump, meaning it holds its shape but is not too wet or too dry.

CELLULAR LIGHT WEIGHT CONCRETE BLOCK

CLC

MIX DESIGN

FOR 1 CUBIC METRE CLC:

Oven-Density in KG/m3:	400	600	800	1000	1200	1400	1600	2350 Conv. Concr.
Sand                                                  (kg)	-	210	400	560	750	950	1100	1950
Cement                                             (kg)	300	310	320	350	360	380	400	320
Water in mortar                              (kg)	110	110	120	120	140	150	160	180
Quantity of Foam                           (Ltrs)	(800)	(715)	(630)	(560)	(460)	(370)	(290)	-
Water in Foam                                (kg)	64	57	50	45	37	30	23	-
Wet Density                                  (kg/m3)	474	687	890	1075	1287	1510	1683	2400
Foaming Agent use                        (kg)	1.5	1.4	1.2	1.1	0.9	0.7	0.6	-
Water/Cement Ratio	0.58	0.54	0.53	0.47	0.49	0.47	0.46	0.56
Maximum Strength                   (N/mm2)	~ 1	~ 2	~ 3	~ 4	~ 8	~ 12	~ 18	25 +
Average Lambda                      (W/m x K)	0.096	0.18	0.21	0.32	0.405	0.45	0.55	2.1

 

(Achieved strength at the lab with optimum sand and cement qualities) More cement will increase strength. Using lightweight aggregate in matrix of Cell.

Concrete increases strength up to 500% in overall densities below 1000 kg/m3

GENERAL REMARKS

Recommended weight of foam              Minimum 80 g/ltr

Crushed Sand might mechanically destroy part of the foam

Water to process foam                                    Potable, if possible below 25 degree celcius

Dilution of foaming agent                                1 part of Neopor to 40 parts of water

Recommended Cement                                   Portland CEM I 325R or higher grade, or similar

Recommended Sand                                         Washed river sand, Density/Sieve: Up to 1000/up to 2mm

                                                                              Minimum 15-18% fines                     Up to 1200/up to 4mm

                                                                              Upto 1400/up to 5mm                      Up to 1600/up to 6mm

1 kg of Neopar foaming agent, diluted in 40 parts of water

Yields approx 510 litres of foam at 80 grams/litre

Captive densities are oven-dry (24h at 100 degree celcius)

Appr. 25% of the total volume of water (in mix and in foam)

in relation to the weight of cement used will crystallize and

therefore will have to be added to the dry-weight of the cement

and sand used to reach the “oven-dry” density.