Материал: Russian Journal of Building Construction and Architecture

Russian journal of building construction and architecture

DESIGNING AND CONSTRUCTION OF ROADS,SUBWAYS,

AIRFIELDS,BRIDGES AND TRANSPORT TUNNELS

UDC 625.7/.8

B. A. Bondarev1, L. A. Prozorova2, Yu. V. Shtephan3

STONE MATRIX ASPHALT BASED ON A CUBE-SHAPED SLAG RUBBLE

Lipetsk State Technical University

Russia, Lipetsk, tel.: +7(474)2-328-083, e-mail: ialex-86@mail.ru, www.stu.lipetsk.ru, 1D. Sc. in Engineering, Prof. of the Dept. of Building Materials

Bellelli Emirates Engineering General Contracting LLC Project

Abu Dhabi –– UAE, Airport Road –– SJ Tower, Suite 10, tel.: +971.244.55830, e-mail: lyudmila_prozoro@mail.ru, www.bellellieng.com

2Manager PhD

Automobile and Road Construction State Technical University (MADI), Russia, Moscow, tel.: +7(499)155-03-30, e-mail: shtephan@madi.ru, www.madi.ru

3Assoc. Prof., Dept. of Production and Maintenance of Automobile and Road Building Machines, PhD

Statement of the problem. This work considers stone matrix asphalt based on cube form blastfurnace cast slag rubble manufactured using modern cone crushers, investigates their properties and compositions and determines pavement durability.

Results. The properties of blast-furnace slag rubble tests are shown as wellas the results of tests of asphalt compositions based on this rubble properties. The outcomes of major maintenance of stone matrix asphalt based on blast-furnace slag implementation in the streets of Lipetsk are presented. This asphalt compositionhasincreasedpavementbearingcapacity.Thedurabilityofthispavementwasinvestigated. Conclusions. Domestic and foreign cube-shaped rubble optimal shape delivering practice allows one to produce rubble on modern secondary and tertiary crushing machines by crushing-separating equipment operation optimization. The optimal rubble is the one with lamellar and needle particles content lower than 10 %. It is experimentally determined that the first group rubble production is considered not effective. It is shown that blast-furnace slag rubble usage at SMA production allows one to deliver a high-quality pavement top layer with no less than 10 years’ life cycle.

Keywords: cast slag rubble, asphalt based on slag, cone crusher, screening, fractions, cube form, rutting.

Introduction

Traffic speeds and loads on pavements have increased over the recent years. Therefore it has become essential to increase the bearing capacity of pavements.

© Bondarev B. A., Prozorova L. A., Shtephan Yu. V., 2017

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It requires the use of more durable and reliable deformation and rutting resistant road building materials. These materials have to be resistant to moisture and abrasion.

Previous maintenance of urban roads and highways in Lipetsk and the region showed that asphalt based on substrate of cube cast slag rubble has such properties. This rubble is delivered with the use of layered drain and slow cooling for crystallization of blast-furnace cast slag with the basicity module less or equal to 1. Rubble is made cube-shaped by means of modern import crushers of Sandvik RC 3800 type. It provides 5––15 mm grains mostly cube-shaped ones and the minimal content of lamellar and needle grains because GOST 8267-93 makes increased demands on these types of grain content within rubble. Modern Hydrocone cone crushers made by Swedish brand Sandvik meet these requirements.

This equipment feature is eccentricity change ability for rubble quality regulation depending on the properties of base rock. Sandvik Roadclassfier RC-3800 crusher is set to operate with granite rubble at dumping slot of 12 mm. It allowed one to obtain the second-group rubble by lamellar grains in a mix of 5––10 mm and 10––15 mm fractions with a 15––40 mm fraction at input.

There are advantages of blast-furnace cast slug rubble:

––Increase in plastic deformations and rutting durability. It is proved by foreign researchers also [1, 4––7];

––Increased rubble grains surface porosity that allows bitumen to stream in pores and improves adhesion;

––Acid blast-furnace slag resistance to all types of self-decay (silicate, calcareous, ferrous);

––Lack of rubble grains polishing that allows one to form micro roughness of pavement and improve friction between tire and surface on wet road.

There are disadvantages of blast-furnace cast slug rubble:

––Decreased strength and abrasion compared to granite rubble although compressive strength at pressing at a cylinder could reach 900––100 grade depending on crystallization level;

––Dust particles formation during rubble less than 20 mm production;

––Demand of bitumen binder consumption increase for steady high porosity substrate grains coating [6].

As it was previously showed [2], these disadvantages could be decreased by adding modifiers in an asphalt mix and by attaching a cube shape to rubble grains. In the present work we set out to optimize based on cube slag substrate asphalt composition, to determine its physical mechanical properties and to predict the durability of SMA pavement.

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Russian journal of building construction and architecture

Earlier we showed blast-furnace slag usage in SMA composition expediency. For producing cube form rubble there is screening dust loaded to input from previous crushing stage (of jaw crusher) with a maximum particle size of less than 70 mm. A stone of more than 15mm fraction falls in operational crushing chamber to provide maximal secondary crushing facility performance. A fraction of less than 15 mm is loaded at once on a conveyer to separator passing crushing chamber. Wherein only +15 mm fraction falls in operational chamber. Therefore a disadvantage of this crusher is that there might be lamellar and flakiness particles with size of 5––15 mm left on the input from previous crushing stages to vendible fractions.

When bitumen and cube slag materials come in contact, the physical and chemical sorption bonds strongly hold bitumen membrane on the surface of a mineral aggregate. Slag surface porosity leads to binder and its components filtration into rubble grains when mixed with bitumen. Wherein oils penetrate grains to the maximal depth. Less fluid pitches penetrate to less depth. Therefore bitumen surface layer on slag grains is enriched with an asphalt that increases the surface strength, heat and wear resistance of SMA. Due to bitumen components and selective filtration there is formation of stiffer and less elastic bitumen membranes on slag aggregate that increase the SMA density [3]. Physical, chemical, electrostatic and diffusional processes occur. As a result, adhesive bonds on bitumen –– aggregate border become more durable and resistant to an environmental influence at the mixing moment and during further time. Blast-furnace slag rubble could be used for SMA-10, 15 and 20 hot production. Slag sands and granulated slags are not recommended for asphalt production due to their low strength. However, large and small same chemical and mineral structure aggregate usage contributes to denser and monolith conglomerate if quartz sand that has the above disadvantages is used [3].

As can be seen, it is clear that there are unsolved problems of optimal compositions delivering and asphalt based on slag cube rubble durability prediction. This shape of the grains allows one not only to decrease expensive bitumen binder consumption but also to reduce pavement rutting and increase its strength and wear resistance as well as proved in [5––7].

Slag rubble cube form industrial production

At first the properties of blast-furnace cast slag aggregate were investigated. It is determined that granulometric composition of cube-shaped rubble delivered on Hydrocone industrial cone crusher made by Swedish brand Sandvik meets GOSTs requirements on lamellar form grains and could be used in the SMA composition.

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The physical and mechanical properties of the resulting rubble compared to those of granite rubble were determined. The results are shoen in Table 1 that shows that blast-furnace slag rubble has no worse properties than does granite rubble.

Practical studies showed that two crushing stages in that type of crusher are not enough for the production of cube-shaped slag rubble. Interim stage for providing operation under block on crushing third stage is necessary to allow the production of a 15––40 mm fraction. Wherein flakiness particles of less than 10––12 % content at all of slag and cube rubble vendible fractions. Therefore it is justified and approved that there is a possibility to obtain blastfurnace cast slag rubble of the average II class using flakiness grains content. Grain form improvement is possible by interim crushing as well.

Slag rubble based on designing SMA pavement

The experiment was planned in order to optimize the SMA composition not by substrate expense only but also using a modifier and bitumen binder. In a mineral mix composition whose components ratio was determined by means of the maximum aggregate density, there was 65 % of less than 5 mm sand fraction and 35 % of 5…10 (5––15) mm fraction slag rubble, other materials were added over 100 % of a mineral mix. In order to optimize the SMA composition the experiment was performed and planned as a three-factor orthogonal central composition (OCCP). Wherein there are the following SMA-15 regression equations:

for compressive strength at 20°С response, MPa:

у1 = 3.72 + 0.117х1 + 0.079х2 + 0.028х3 – 0.073х1х2 + 0.057х2х3 + 0.234х12 – 0.091х22, (1)

for compressive strength at 50°С response, MPa:

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Russian journal of building construction and architecture

for crack resistance:

у5 = 3.512 – 0.155х1 + 0.1х2 – 0.209х3 + 0.034х1х2 – 0.041х1х3 – 0.008х12 + 0.029х22. (3)

These formulas allow one to predict blast-furnace slag based SMA properties depending on the composition. The optimal SMA composition was implemented in 2012 during major maintenance of highways in Lipetsk. For this purpose pavement with the investigated composition based top layer development was implemented. “Civil Project of Lipetsk” Plc, developed pavement construction scheme construction scheme includes: stone matrix asphalt SMA-15 –– 4 cm; B type dense coarse-graded hot mix asphalt based –– 6 cm; II mark asphalt treated permeable bases –– 8 cm; bound black chippings –– 10 cm; bound graded rubble made of dense rock –– 15 cm; sand (GOST 8736) –– 30 cm; soil (heavy loam). Layers thickness calculations allowed one to reduce the thickness of the top layer from 5 to 4 cm without decreasing its bearing capacity by means of the SMA increased density and strength. For SMA deformability assessment elastic modulus calculations were performed. The construction meets the requirements for the durability and reliability by the elastic modulus value given that:

where Еtl and Emin are the estimated total and minimal required elastic modulus of apavement, MPa; Кnel is a strength safety factor by means of the elastic modulus criteria, for the reliability level 0.98 Кnel = 1.

The necessary total elastic modulus was calculated by means of the following formula:

where ∑Np is a total of an estimated load applications number for a pavement life cycle; с is an empirical parameter for the estimated axis load of 100 kN which is с = 3.55. By means of Formula 5, the estimated elastic modulus was obtained:

Emin = 98.65 [lg∑Np – c] = 98.65 (lg1022958 – 3.55) = 242 MPa.

The elastic modulus of pavement layers was identified when calculating using the allowable elastic deflection at 20 °С and when calculating monolith layers for bending at 10 °С. A structure based on a granite rubble with 4 cm of SMA-15 top layer meets the requirement for strength using the allowable elastic deflection. The strength safety factor is Кnel = 1.06.

It is shown in the course of the calculations that SMA based on slag aggregate has a higher load capacity compared to SMA based on granite rubble when the thickness decreases from

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