Characteristics of High- Strength Concrete for

Transcription

1 Optimizing Paving Concrete Mixtures and Acceerated Concrete Pavement Construction and Rehabiitation Study on Factors Infuencing Characteristics of High- Strength Concrete for Airport Pavements Yoshitaka Hachiya (Port and Airport Research Institute), Junichi Noda, Shoichi Kameta, Takashi Tochigi, Yukitomo Tsubokawa, Ryota Maekawa and Yasushi Takeuchi Background & Objectives Recent socia requirements resource saving construction cost reduction onger service ife, etc. For airport pavements decreasing concrete sab thickness increasing i concrete strength th strengthening the foundation Use of high-strength concrete presenty specified design fexura strength: 5 N/mm 2

2 Background & Objectives (cont d) For reinforced concrete structures high-compressive-strength concrete in genera use risks in its direct appication to airport pavements High-strength concrete for airports sufficient workabiity and finishabiity ow construction cost Contents New researches to study the appication of high-fexura-strength concrete to airport pavements with neither specia materias nor construction methods Study pan aboratory tests experimenta construction Research resuts Properties of high-fexura-strength concrete Mix design appropriate for airport pavements Workabiity of concrete in paving works

3 Materias Used in This Study Materia Cement Fine aggregate Coarse aggregate Admixture Description Ordinary Portand cement Sand Hard sandstone, imestone and andesite High-range water-reducing AE admixture and retarder 5 Laboratory Tests Coarse aggregate & water-cement ratio to obtain the high-strength concrete Unit water content, t fine aggregate, coarse aggregate and admixtures to obtain the sufficient workabiity Possibe high-strength concrete mix proportions tentativey seected The appicabiity to actua construction work evauated with a sma construction machine (mini-finisher) i i The optimum mix proportion determined by observing the finished surface 6

4 Evauation of Concrete Properties State Hardened Fresh Item Fexura strength Sump Air content Consistency Workabiity Finishabiity 7 Workabiity Test with Vibration Pate Vibration machine vibration mass: 30 kg, frequency: 4,000 rpm, excitation power: 1.4 kn Quantified by the WF-vaue cacuated from the thickness of mortar emerged on the pate after 60 s vibration 8

5 Finishabiity Test with Mini- Finisher Construction Test Device Paced in a form 1.6 m in width, 1 m in ength and 150 mm in thickness Quantified by observing the concrete surface after the finishing screed passed examining the resistance to screed movement with measuring the strain on its drive shaft 9 Curing for Simuating the Environmenta Conditions Covered with a sheet for 30 minutes, then time for transportation Directy exposed for 60 minutes to simuated sunight (using amps) and wind (provided by fans), without the sheet time from concrete arriva to finishing work 10

6 Infuence of Coarse Aggregate on Fexura Strength Characteristics of Coarse Aggregates Type Property Size (mm) Density (g/cm 3 ) Absorption (%) Unit Crushing Wear weight vaue (%) (kg/l) (%) G-1 Hard sandstone G-2 Hard sandstone G-3 Andesite G-4 Limestone G-5 Hard sandstone Limestone Aggregate Crushing Vaue and Concrete Fexura Strength 2 ) Fexura a strengt th (N/mm High-strength Standard Crushing vaue (%) High-strength concrete with coarse aggregates of ower crushing vaue exhibits higher fexura strength. In standard-strength concrete, coarse aggregate crushing vaue barey has an infuence on concrete fexura strength. 12

7 Infuence of Factors on Properties of Fresh Concrete Unit Water Content Characteristics of Fine Aggregate Characteristics of Coarse Aggregate Type of coarse aggregate has itte infuence on the workabiity of high-strength concrete. 13 Variation in Consoidation Time with Unit Water Content time (s) Conso oidation 50 W(kg/m 3 ) Time unti test (min) Consoidation time increases with a decrease in -unit water content, t and - time to the test. Concrete with very good workabiity is obtained by maintaining a sufficient unit water content. 14

8 Characteristics of Fine Aggregate Percent passing Density Absorption Aggregate (g/cm 3 Fineness ) (%) moduus S S Sump and Amount of Admixture S1 S2 p (cm) Sum Amount of admixuture (percent of unit cement content) Concrete sump varies greaty with type of fine aggregate. Sump increases with the amount of admixture. 16

9 Change of Sump with Time - to obtain a sump of 8 cm at 30 min after preparation - ump (cm m) S Time after preparation (min) S1 Sump of concrete with S1 S2 is arger than that with S2 just after preparation, but becomes smaer than that with S2 90 minutes after preparation. Fine aggregate S2 is more advantageous than S1. 17 Adjustment of Super-Fine Aggregate Amount Characteristics of Fine Aggregates for Mortar Aggregate Percent passing Fineness moduus S S1-a S1-b S1-c Gradation was adjusted d by decreasing the proportion of super-fine aggregate (passed mm sieve ). 18

10 Super-Fine Aggregate Ratio and Amount of Admixture dmixture cement) ount of ad rcent of c Amo (per S1 The amount of S1-a S1-b S1-c Super-fine aggregate ratio (%) admixture is greaty different between the tested fine aggregates. Super-fine aggregate has a considerabe effect on the amount of admixture. 19 Evauation of Finishabiity of High-Strength Concrete Suitabe mix proportion for high-strength concrete was examined in ight of workabiity in pavement construction Mini-finisher tests were conducted with high- strength concretes with various mix proportions. Unit water content was set at 115 to 125 kg/m 3 Concrete surface coud not be finished satisfactoriy under the simuated environmenta condition. 20

11 Modification of Mix for High- Strength Concrete Unit water Item content was No.1 increased No.2 to No.3 135kg/m(type) 3. SP-a SP-b High-range water-reducing AE admixture (amount) Retarder Two different high-range water-reducing AE admixtures were added. Sump (cm) 8.5 / 3.5 / / 3.5 / / 8.0 / 4.0 Aggregates were changed. Air content (%) * 4.3 / 2.8 / / 3.0 / / 3.4 / 2.5 Retarder was introduced. WF vaue (mm) < 2.3 < Axia force of shaft (kn) Visua evauation of surface Poor Good Fair * immediatey / 30 min / 90 min after concrete preparation 21 Determination of Appropriate Mix Proportions Appropriate Mix Proportions of High-Strength th Concrete Mix W/C V G s/a Unit voume (kg/m 3 ) AA proportion (%) (m 3 /m 3 ) (%) (cm W C S G HWR RE 3 ) A B Change in Properties of Fresh Concretes with Time Mix proportion Eapsed time since preparation when tested Immediatey 30 min 90 min Sum Air Sum Air Sum Air WFvaue p content p content p content (cm) (%) (cm) (%) (cm) (%) (mm) A < 2.3 B

12 Paving Work with High- Strength Concrete High-strength concrete Fexura strength: 6.5 N/mm 2 Sab thickness: 340 mm Section C (Sections A & B for trias) Standard d concrete Fexura strength: 5.0 N/mm 2 Sab thickness: 420 mm Section D Paving works Evauation of paving process Observation of pavement surfaces Experimenta Pavement Construction Pan 7.5 A B C D (unit: m) High-strength Standard A B C D Section (unit: mm) Concrete sab Base Subbase Subgrade

13 Concrete Properties in Design Specified Mix Proportions of Concretes Concrete W/C (%) V G (m 3 /m 3 ) s/a (%) Sump (cm) Air content (%) Unit content (kg/m 3 ) Admixture W C S G HWR RE WR AA Highstrength , A Standard , A Characteristics of Concretes Concrete Sump (cm) Air content (%) Fexura strength (N/mm 2 ) 7 d. 28 d. High-strength th Standard Paving Works for High- Strength Concrete Transported by dump trucks covered with pastic sheeting for about 30 min. Spread in two ifts, with a ower ift of 230 mm and an upper ift of 110 mm. No interna vibrator was used for the upper ayer, but the ower ayer was vibrated. Wire mesh was paced over the ower ift. The upper ift was compacted using the concrete finisher at a rate of 80 cm/min. Cured by the conventiona method using mats and water spraying. 26

14 Paving Works for Standard Concrete Transported within 15 minutes. Spread in two ifts, a ower one of 280 mm and an upper one of 140 mm. Concrete compaction, use of wire mesh, and surface curing foowed the procedures used for high-strength. g 27 Timetabe of Concrete Sab Construction High-strength Standard High-strength concrete is equa in workabiity and finishabiity to the standard. Finishing and curing has to be initiated sooner than the standard. 28

15 Properties of Concretes Characteristics of Fresh Concretes Item Section C Section D Pant Site Pant Site Sump (cm) 8.7 (7 9.5) 5.4 (3 7.1) 5.4 ( ) 2.6 ( ) Air (%) 48( ) 5.5) 38(3 3.8 (3.2 45) 4.5) 36(3 3.6 (3.2 40) 4.0) 33(3 3.3 (3.0 36) 3.6) Temperature ( C) 9.2 ( ) 5.7 ( ) Air temperature ( C) (25 31) (18 20) Strength of Hardened Concretes 78N/ 7.8 N/mm 2 at tsection C 6.0 N/mm 2 at Section D after twenty eight days of curing 29 Observation of Pavement Surfaces Cracks might have resuted from inadequate curing as the area was the portion constructed at the end of the day. at Section C (high-strength concrete) 30

16 Evauation of Cracks at Section C Structura Evauation with FWD Concrete Position Surface D 0 temp. (mm) ( C) High- Interior strength Joint Corner Interior Standard Joint Corner Cracks neither propagated further nor widened after one year. Sabs were structuray sound according to defections measured with FWD. 31 Summary and Concusion On infuencing factors on the properties of highstrength concrete and its optimum mix proportion Fexura strength increases with a decrease of coarse aggregate crushing vaue. Consoidation time and its change with time decrease with an increase of water content. Decrease of super-fine aggregate is effective to ensure sufficient workabiity. Coarse aggregates have itte infuence on the fresh properties. An optimum mix proportion was determined that met the requirements for airport pavement construction.

17 Summary and Concusion (cont d) The appicabiity of the new high-strength concrete to airport concrete pavement construction was examined through experimenta construction. Concrete sabs with high-strength concrete can be constructed in the same way as with standard concrete. The concrete shoud be cured sooner as compared with the standard strength concrete. The behavior of a high-strength concrete sab under natura environmenta conditions and its bearing capacity are amost same as of the standard d concrete sab.