The Impact of the Quantity and Type of Plasticizer on Basic Technical Characteristics of Concrete Paving Stones

Transcription

1 Jan Antoni Rubin, PhD, Eng, Politechnika Śląska, Gliwice, [Silesian University of Technology, Gliwice] The Impact of the Quantity and Type of Plasticizer on Basic Technical Characteristics of Concrete Paving Stones This article presents the results of technological tests conducted in order to determine the impact of the quantity and type of the specific plasticizers on the basic technical characteristics of concrete paving stones. Two plasticizers were used during the tests, dosed at % of the cement weight. Values for the following technical characteristics were determined: splitting tensile strength, compressive strength, capillary suction and water absorption. Admixtures have already been used in ancient times (e.g. Egypt, Mesopotamia, Greece and in the Roman Empire) to modify lime matrix composites. The admixtures available at that time include: dairy products (mainly caseins), eggs because of their protein content, cereals (the main ingredient of which is starch) and sometimes also vegetable oils and animal fats with their primary glyceride ingredient, i.e. esters of organic acids saturated and unsaturated with glycerin [9]. From the perspective of their chemical composition, the above-mentioned natural admixtures, which give plasticity at the time of application and strength and durability during operation, are composed of carbohydrates, hydrocarbons and amino acids [9]. Chemical concrete admixtures, in accordance with the standard PN-EN 943-2:2009 [7], are substances recommended to be added to concrete mixtures during preparation. The said admixtures are added to the concrete mix to modify its physicochemical properties and the technical characteristics of the hardened concrete [2]. The use of chemical admixtures only makes sense in the case of professionally designed concrete mixtures. Chemical admixtures must not exceed 5% of the weight of the cement and can generally be divided by their mode of functioning into [2, 3]: plasticizers (water reducing admixtures) superplasticizers and liquefiers (admixtures significantly reducing the amount of water) air entraining admixtures set-retarding admixtures hardening and/or set-accelerating admixtures sealing admixtures complex admixtures (liquefying and air entrainment or liquefying and accelerating admixtures and antifreeze admixtures) Symbol Name of plasticizer Chemical base Recommended dose (by manufacturer) (% cement mass) C Procon Plus (BV) lignosulfonates ,8 ± 1,0 D Procon Pave (BV) lignosulfonates and surfactants ± 1.0 Tab. 1. Basic technical parameters of the plasticizers used Technical characteristic Unit ph Plasticizer/percentage C 0.4 C 0.2 C 0.1 D 0.4 D 0.2 D 0.1 f r after 1 day MPa f r after 7 days MPa f r after 22 days MPa f r after 28 days MPa f c after 1 day MPa f c after 7 days MPa f c after 22 days MPa f c after 28 days MPa p * k mm n w (max.) % 5.06 ( 5.22 ) 4.91 ( 5.11 ) 5.19 ( 5.27 ) 5.00 ( 5.13 ) 6.10 ( 6.38 ) 5.63 ( 5.73 ) Tab. 2. Determined average values of the selected technical attributes of six concrete series * Height measured from the initial water level (maximum values are presented)

2 after 1 day after 7 days after 22 days after 28 days Fig. 1. Average splitting tensile strength for six concrete series with two different plasticizers after 1 day after 7 days after 22 days after 28 days Fig. 2. Average compressive strength for six concrete series with two different plasticizers

3 Nowadays it is difficult to imagine modern road construction without concrete with cement matrix. To imagine this cement matrix without modifications from new generation admixtures, i.e. superplasticizers and air entraining admixtures, is just as difficult [9]. The said admixtures are used in the production processes of concrete products formed using various modern methods. Generally, these methods for concrete compaction can be divided into three groups [6]: non-vibration methods (pressing, swirling, implosive compaction, vacuum compaction, roll compaction) vibration methods (shaking, vibration, impulse compaction) combined methods (pressing and deaeration, vibration and deaeration, vibro-pressing, vibrorolling) In the production of small-sized concrete elements (such as cobblestones, curbstones and pavements, palisades, etc.), the vibro-pressing technology enables to obtain a sufficiently high compaction of the concrete mix and concrete, while maintaining a low water/cement ratio (w/c) [1]. Such production, however, requires the use of plasticizers which increase the liquidity of mixtures based on cement binders (when w/c rate = constant) [5]. It should be mentioned that in fact a number of factors affect the correct consistency of the concrete

4 mix as well as the high early strength of the concrete material. These factors are: type and amount of cement type and size distribution of the aggregate water/cement ratio (w/c) temperature of the concrete mix and the environment geometrical dimensions of the prefabricated element method and intensity of care type and percentage of the admixtures applied to the concrete mix

5 Scope and Purpose of the tests The technological tests were conducted to determine the impact of selected plasticizers on the basic technical characteristics of concrete paving stones and are a continuation of earlier tests [8]. The applied plasticizing admixtures are organic substances with surface-active and hydrophilic properties (the so called surfactants), they partially neutralize electrical charge on the surface of the cement grains [5]. The plasticizer molecules are adsorbed on the surface of the cement grains which are dispersed afterwards [4]. Tab.1 presents the basic technical parameters of these plasticizers. The concrete mix was formed from 0-8 mm aggregate, CEM I 42.5R Portland cement, tap water and two selected plasticizers (symbols: C and D). Each plasticizer was dosed at 0.4, 0.2 and 0.1% of the cement weight. The tests were performed on a technological line manufactured by AME (Austria), in double layer technology for molding on production and transport tables. The basic ingredients of the concrete mix used for each test were supplied by the same manufacturers and suppliers. They were initially tested in the laboratory to eliminate possible qualitative differences. At the end of the technological test, the values of the following technical features were determined (and presented in Tab. 2): a) splitting tensile strength (f) - for 8 samples for every composition and date of tests b) compressive strength (fc) - for 5 samples for every composition and date of tests c) capillary suction (pk) - for 3 samples for every composition d) water absorption (nw) - for 3 samples for every composition The main purpose of the technological tests was to obtain optimal technical parameters for the products, in particular better capillary suction (mainly due to efflorescence) and water absorption (frost resistance). At the same time it was assumed that the strength should not suffer significantly. A possible improvement of the workability of the concrete mix and consequently an improved efficiency of the technological production line was important as well.

6 Fig. 3. Maximum values of capillary suction of water for six concrete series with two different plasticizers Fig. 4. Average values of water absorption for six concrete series with two different plasticizers Summary The results of the technological tests show that the Procon Plus (code symbol C) and Procon Pave (code symbol D) plasticizers have similar cement matrix modifying properties. However, for concrete production a cement matrix modified with the Procon Plus plasticizer, dosed at 0.2% of the cement weight is mainly recommended. At this point it should be emphasized that the exact dosing depends on the required concrete properties in the particular case and should be determined by pre-testing with the anticipated raw materials. The final results in each specific case depend also on the specific production line, the predefined technical parameters and the components used.

7 Literature 1. Brylicki W.: Paving Stone Made of Vibro-pressed Concrete. Polski Cement, Kraków Gołaszewski J.: Concrete Admixtures. Magazyn Autostrady, 8-9/ Jamroży Z.: Concrete and its Technologies. Warsaw Jasiczak J., Wdowska A., Rudnicki T.: Ultra High Performance Concrete. Polski Cement, Kraków Łukowski P.: Mortar and Concrete Admixtures. Polski Cement, Kraków Mikoś J.: Selected Issues in Prefabrication Technology. Warsaw PN-EN943-2:2009 Concrete, Mortar and Cement Grout Admixtures - Part 2: Concrete Admixtures. 8. Rubin J.A.: Impact of Selected Plasticizers on Basic Technical Characteristics of Concrete Paving Stone. Magazyn Autostrady, 3/ Rudnicki T.: Natural and Synthetic Plasticizing Admixtures and the Mechanisms of their Action in Concrete Mix. Magazyn Autostrady, 4/2004.