50号道路石油沥青 · Bitumen 50# for High-Temperature Zones and Heavy Loads

50号道路石油沥青按JTG F40-2004分级，针入度40–60（0.1mm），A级软化点不低于49 °C，闪点不低于260 °C，溶解度不低于99.5 %，蜡含量不大于2.2 %，老化后残留针入度比不低于63 %，是常用标号中最硬的一档。牌号数字是名义针入度，不是区间端点。它主要用于夏季高温区的高速公路面层、重载与渠化交通路段、长大纵坡、收费广场和港区道路。冬冷夏热并存的气候分区不能靠加硬牌号解决，应当选用聚合物改性沥青。

50# road petroleum asphalt is graded under JTG F40-2004 with a penetration band of 40–60 (0.1 mm). For A级 the softening point is minimum 49 °C, flash point minimum 260 °C, solubility minimum 99.5 %, wax content maximum 2.2 % and the retained penetration ratio after ageing minimum 63 %, stricter than the figure asked of any softer grade in the table. Read 50 as a nominal penetration sitting at the centre of the 40–60 band, not as one of its limits — the reverse of the ASTM 40/50 convention. 50# is the hard grade for high-temperature regions and heavily loaded pavements: expressway surface and middle courses in hot zones, long steep grades, toll plazas, bus bays, port-area roads and other channelised heavy-truck loading. Where a climate zone code carries both a hot summer digit and a severe winter digit, the answer is a polymer-modified binder rather than a harder penetration grade.

The governing document is JTG F40-2004《公路沥青路面施工技术规范》 — a Ministry of Transport construction specification for asphalt pavements, inside which the binder requirement table is one clause of a much larger works document. Within it, 50# means penetration 40 to 60 (0.1 mm) at 25 °C, 100 g, 5 s, run to method T 0604 of JTG E20-2011《公路工程沥青及沥青混合料试验规程》. The digits 50 name the 标称针入度 — the nominal value the band is built around — and no cargo has any obligation to test at 50 itself.

ASTM works the other way round. Under D946 a grade name states its own two limits, so 40/50 admits 40 to 50 dmm and nothing beyond. Set the two windows against each other and the asymmetry is arithmetic: the Chinese window is twenty tenths wide, the American one is ten, and the American one sits wholly inside it. 50# is therefore not a rename of ASTM 40/50. A trader who uses the two names interchangeably will sooner or later reject a perfectly compliant 50# cargo for being too soft, or load a 56 dmm batch against an ASTM 40/50 purchase order and learn about it from the destination laboratory.

硬端的相对带宽 · The proportional tolerance widens toward the hard end

Across the paving grades from 30# to 130# the acceptance band is 20 dmm wide in every case. That fixed width means very different things at different points on the ladder, because it is measured against a different nominal value each time. At 130# a 20 dmm band is roughly ±7.7 % about the nominal. At 70# it is ±14 %. At 50# it is ±20 %, and at 30# it is ±33 %. Of the grades in routine paving use, only 30# is proportionally looser than 50#.

The practical consequence is worth stating flatly: a 40 dmm cargo and a 60 dmm cargo are both fully compliant 50#, and one is 50 % softer than the other. Two batches that carry the same grade name will not behave the same way in the mix design, in the compaction window or in the pavement. On a project where 50# was chosen specifically for deformation resistance, the buyer should be looking at the actual penetration figure on the Certificate of Analysis and at where in the band it sits, not merely at whether the grade name matches. Where the design is sensitive, it is legitimate to write a narrower acceptance range into the contract than the standard requires — the standard sets a floor for compliance, not a ceiling on what a buyer may specify.

硬端的两个台阶 · Reading the ladder from the hard end down

The numbering runs against hardness — a bigger number is a softer binder. What a 50# buyer needs from the series is not the whole list but the shape of two requirements as they move toward the hard end, because those two are what a hard grade is actually being sold on.

The softening point floor climbs, and it climbs unevenly. Between 110# and 70# it moves three degrees in total — 43, then 45 at 90#, then 46 at 70#. Then it jumps three degrees in a single step to 49 at 50#, and six more to 55 at 30#. The A级 floors are flat across the soft half of the series and steep across the hard half, which is exactly what one would expect of a family where the soft grades are chosen for low-temperature behaviour and the hard grades are chosen for high-temperature behaviour. A buyer moving from 70# to 50# is not buying an incremental improvement; the specification itself treats it as a step change.

The flash point floor does not move at the hard end at all. 260 °C applies at 70#, at 50# and at 30# alike, and it only relaxes going the other way — 245 °C at 90#, 230 °C at 110# and 130#. So a 50# is held to precisely the same flash point requirement as the mainstream grade, and that requirement sits 28 °C above the ASTM D946 minimum of 232 °C. For an exporter that is the practical point: hardening the grade buys nothing in flash point headroom, and the 260 °C line has to be cleared on its own merits. With solubility at 99.5 %, it is one of the two requirements an ASTM-built export certificate most often fails on paper before wax content has even been looked at.

Two grades sit at the ends of this page’s argument and are treated only as reference points. 30# (penetration 20–40, softening point minimum 55 °C) is a structural stiffness choice for high-modulus work rather than a general paving grade; 90# (penetration 80–100, softening point minimum 45 °C for A级, flash point minimum 245 °C) is what a project reaches for when winter, not summer, governs. The softer grades below 90# and the seldom-traded top of the series have their own pages and are not restated here.

A级、B级、C级 · The class question, which is usually already answered at 50#

The A/B/C quality class structure is China-specific and has no ASTM or EN counterpart. The class does not change the penetration band — 50# is 40–60 whether it is A级, B级 or C级, so the one line an exporter is certain to have on his certificate is also the one line that proves nothing about class. The class is carried instead by the wax ceiling (蜡含量), by ductility at 10 °C, by the penetration index window (针入度指数) and by the requirements imposed on the residue after ageing. The class then governs permitted use:

• A级 — unrestricted: every grade, every pavement layer, every class of road.
• B级 — admitted to the lower layers (下面层及以下层次) of 高速公路 and 一级公路, and to every layer of roads below those classes.
• C级 — admitted from 二级公路 downwards.

At 50# this ordinarily settles itself. The reason a project reaches for a hard grade is heavy traffic on a high-class road, and the layer that carries the deformation is the surface or middle course of an expressway or class-1 highway. That is exactly the position B级 is excluded from. So on most genuine 50# enquiries the answer is A级, and the commercially convenient fallback of offering B级 material against a marginal wax result simply does not exist. Confirm the permitted-use clause against the edition of the specification named in your own project documents, and ask the buyer which layer of which highway class the binder is going into before anything else.

第二套标准 · GB/T 15180 and AH-50

Alongside JTG F40-2004 sits GB/T 15180《重交通道路石油沥青》, and the difference between the two is a difference of kind before it is a difference of numbers. GB/T 15180 is a national product standard — it exists to say what a heavy-traffic road petroleum asphalt must be, full stop — where JTG F40-2004, as set out at the top of this section, is a works document whose binder table is one clause among many. One defines a material; the other governs an operation that happens to consume it. GB/T 15180 labels its grades in an AH- series running AH-130, AH-110, AH-90, AH-70, AH-50, AH-30, and AH-50 stands at the nominal position corresponding to 50#. That correspondence of position is where the similarity ends.

For this grade in particular the second standard deserves a check rather than a footnote. The title of GB/T 15180 — heavy-traffic road petroleum asphalt — describes exactly the loading condition that causes an engineer to specify 50# in the first place, so a heavy-duty project is more likely to be written against it here than at the softer end of the ladder. The two documents are not interchangeable labels for a single requirement set. They part company on solubility, on the shape of the softening point requirement, on the wax ceiling and on post-ageing mass change, and GB/T 15180 carries no A/B/C structure at all — which means AH-50 A级 describes nothing, and a purchase order carrying it has left the acceptance table to be settled at the destination laboratory. Read the AH-50 limits out of the standard itself before offering against them, and write one standard, one edition and — where JTG F40 applies — one quality class into the contract. 50号道路石油沥青，JTG F40-2004，A级 closes far more of the specification than the two characters 50#.

车辙是怎么形成的 · What rutting actually is

车辙 — rutting — is permanent deformation along the wheel path. Chinese pavement practice decomposes it into three contributions: 压密变形, the densification of an under-compacted mat under early traffic; 剪切流动变形, shear flow of the mixture when the binder is too soft to hold the aggregate skeleton in place at high pavement temperature; and 磨耗, surface abrasion. Binder consistency governs the second of these. It has almost no influence on the first, which is a compaction problem, and none on the third.

Two related distresses travel with it. 推移, shoving, appears where traffic decelerates and accelerates over the same patch of pavement — intersections (交叉口), bus stops, toll approaches. 泛油, bleeding or flushing, appears where binder migrates to the surface in hot weather and leaves a slick, dark, low-texture patch. Both are high-temperature consistency failures and both respond to a harder binder.

风险集中在哪里 · Where the risk actually concentrates

Rutting is not uniformly distributed along a road. It concentrates wherever heavy axles spend the most time over the same square metre of surface:

• 长大纵坡 — long steep grades, where loaded trucks crawl uphill and the dwell time per unit area is at its longest. This is the classic Chinese rutting location and a standing reason to specify a hard binder for a specific chainage rather than for a whole route.
• 渠化交通 — channelised traffic, where lane discipline keeps every wheel path in the same track instead of letting loading wander across the lane width.
• 收费广场与交叉口 — toll plazas and intersections, where deceleration adds horizontal shear to vertical load.
• 公交停靠站 — bus bays, a small area taking a very high repetition of heavy, slow, braking axles.
• 港区道路与堆场 — port-area roads and container yards, where container handlers apply concentrated loads at low speed.

动稳定度 · The measure the specification actually uses

China does not accept rutting resistance on a binder grade name. The acceptance measure is 动稳定度, dynamic stability, obtained from the wheel tracking test (车辙试验) under JTG E20-2011 method T 0719 and reported in 次/mm — loading passes per millimetre of deformation. JTG F40 sets minimum dynamic stability values that vary with the climate zone, the highway class and whether the mixture is made with ordinary or polymer-modified binder, and the values required of modified mixtures are substantially higher than those required of ordinary ones. Read the figures that apply to your zone and highway class from the current table.

The point a supplier should be honest about is this: 动稳定度 is a property of the mixture, not of the binder. Aggregate gradation, angularity, filler content, void ratio and field compaction all move the number, and they can move it further than a change of binder grade does. Supplying 50# instead of 70# improves the odds. It does not deliver a dynamic stability result, and no supplier can promise one, because the supplier does not control the aggregate, the plant or the roller pattern. Where a project has a dynamic stability requirement, that requirement is met by a mix design verified in the laboratory with the actual materials — the binder is one input into it.

另一端 · Low-temperature cracking, and what hardness costs

As a pavement cools, the asphalt layer wants to contract. It is restrained by the layers beneath it and by its own continuity, so the contraction turns into tensile stress. A binder that can relax that stress by flowing slightly relieves it; a binder that cannot, does not, and the layer relieves it by cracking. The result is 低温收缩开裂 — thermal shrinkage cracking, seen as regularly spaced transverse cracks (温缩裂缝). A harder binder relaxes stress more slowly and therefore cracks at a higher temperature than a softer one from the same source.

There is a second cost. A stiffer binder in a thin layer over a flexible foundation accumulates fatigue damage faster under repeated bending, which shows up as 疲劳开裂. So hardness is not free at either end of the year: it buys resistance to summer deformation and it spends resistance to winter cracking and to fatigue.

为什么不能靠加硬解决一切 · Why the trade-off cannot be engineered away with penetration alone

The reason is contained in the penetration index. PI (针入度指数) describes 感温性, temperature susceptibility — how sharply the binder’s consistency changes as temperature changes. JTG F40 bounds it to a window of -1.5 to +1.0, which is a wide window: it constrains the binder from being pathologically temperature-sensitive, and it does not make one binder flatter than another in any useful design sense.

Moving down the penetration ladder shifts the consistency-temperature curve. It does not flatten it. A 50# is stiffer than a 70# at 60 °C, and it is also stiffer than that 70# at -10 °C. There is no setting of the penetration dial that gives you the summer behaviour of a 50# and the winter behaviour of a 90#, because the dial only has one axis. Anyone who has been told otherwise has been sold a grade rather than a design.

气候分区代码 · Reading the zone, and the two digits that matter here

JTG F40 gives each project location a three-part 气候分区 code, written like 1-4-1 or 2-2-2. For a hard-grade decision the first two digits carry the whole argument, so take them first and the third afterwards.

第一位 — 夏季高温分区. Derived from the hottest month’s mean maximum air temperature, and it is the digit that puts 50# on the table at all. A 1 means above 30 °C, a 2 means 20 to 30 °C, a 3 means below 20 °C. Only a 1 makes summer deformation the governing distress on its own.

第二位 — 冬季低温分区. Derived from the extreme minimum air temperature, and it is the digit that decides whether the project can afford a hard grade. 1 is below -37 °C, 2 is -37 to -21.5 °C, 3 is -21.5 to -9 °C, 4 is above -9 °C. A hard binder is affordable at 4, arguable at 3, and a liability at 1 or 2.

第三位 — 雨量分区. Annual rainfall: 1 humid above 1000 mm, 2 moist 500 to 1000 mm, 3 semi-arid 250 to 500 mm, 4 arid below 250 mm. It does not drive the penetration choice, but it bears on moisture damage and on the mixture design around the binder.

One reading trap sits underneath all three: the scales do not ascend with severity, they descend. 1 is always the harshest value in its own dimension — hottest summer, coldest winter, wettest climate. A designer who assumes a bigger digit means a harder condition inverts the winter reading, which is precisely the reading a 50# decision hangs on.

50# has one unambiguous home: a hot first digit combined with a mild second digit. A code of the form 1-4-x describes a location with hottest-month mean maximum air temperatures above 30 °C and extreme minima above -9 °C — summer deformation governs the design and winter cracking barely enters it. Add a humid third digit and the pattern 1-4-1 describes the environment of the far south of China: hot, wet, and without a winter severe enough to punish a stiff binder. Combine that with heavy freight and channelised loading and you have the case 50# was written for.

冷热双极的分区 · When the code pulls both ways at once

Now take a code with a hot summer digit and a severe winter digit — a first digit of 1 or 2 alongside a second digit of 1 or 2. This is a real and common condition across large parts of interior and northern China, and it is where grade selection stops being a lookup.

Read only the first digit and you specify 50#. Read only the second and you specify 90#. Both readings are wrong, because the pavement experiences both seasons. Specifying 50# there accepts a low-temperature cracking exposure that the binder’s own stiffness makes worse. Specifying 90# accepts summer rutting under exactly the heavy traffic that prompted the question. Splitting the difference at 70# accepts a reduced version of both risks and may be the honest engineering answer on a lightly loaded road — but on an expressway carrying heavy freight it is a compromise, and it should be recorded as one.

The correct move is to stop travelling along the penetration axis and change the shape of the curve instead. That is what polymer modification does: it raises the binder’s stiffness and elastic response at high service temperature while preserving, or improving, its ability to relax stress at low service temperature — an outcome no unmodified penetration grade can produce, because the unmodified grade has only one dial.

JTG F40-2004 provides for this directly. It carries a separate requirement table for polymer-modified asphalt (聚合物改性沥青), organised by modifier family — SBS as 类 I, SBR as 类 II, and EVA or PE as 类 III — with further subdivisions inside each family. That table asks for properties the unmodified table never mentions, notably 弹性恢复 (elastic recovery) and 离析, the storage stability or segregation check that confirms the polymer has not separated from the base binder on standing. This page does not reproduce the modified-binder limits: they are a different specification with a different acceptance regime, and a supplier who quotes them from memory is the wrong supplier. What matters commercially is the direction of the answer — where the zone code conflicts, the specification’s own route is modification, not a harder number.

There is a related design route worth knowing about, because a buyer may meet it in the project documents rather than in the binder specification. Chinese practice for heavily loaded expressway surfaces in hot zones frequently uses a stone-mastic type mixture (沥青玛蹄脂碎石, SMA) or a high-modulus asphalt concrete (高模量沥青混凝土) to carry deformation resistance in the aggregate skeleton rather than in the binder alone. In those designs the binder grade is fixed by the mixture specification and is not a free choice, so the correct question to a Chinese buyer is never which grade do you want but which mixture type and which specification is the design written to.

50号实际用在哪里 · Where 50# actually goes

• Surface and middle courses (上面层、中面层) of expressways and class-1 highways in hot-summer, mild-winter zones carrying heavy freight.
• Specific high-risk chainages on an otherwise 70# route — long steep grades, toll plazas, bus bays, major intersections.
• Port-area roads, container yards, industrial hardstanding and other slow, concentrated, heavy loading.
• High-modulus base and binder course mixes where the design wants a stiff layer to spread load.
• As a base binder for modified asphalt production in hot zones — noting that in that case the base grade is fixed by the modified-binder specification and is not chosen freely.

50# is also used as the hard component when a target consistency is reached by blending two stocks. One caution belongs with that practice: Chinese acceptance testing is performed on the finished binder as delivered, not on a blend calculation, so a blended product has to be sampled and tested as a product in its own right — including wax content and the ageing residue block — before it is offered against a 50# specification.

What 50# should not be used for is equally worth saying: cold-winter zones, thin surfacings over flexible foundations where fatigue governs the design life, and low-volume county roads where nothing in the traffic justifies accepting the cracking exposure. A hard binder placed where it is not needed does not fail gracefully; it cracks.

63 % 是在哪一步之后量的 · The oven step the ratio is measured after

T 0609 (薄膜加热试验, thin film oven) and T 0610 (旋转薄膜加热试验, rolling thin film oven) hold the binder as a thin film at 163 °C for a fixed period. The oven is not the point; the mixing plant is. A binder is hardened once by the plant before a single truck has driven over it, and the standard wants to know how much of the delivered consistency survives that first insult. Two numbers come out of the procedure. Mass change is held inside ±0.8 % in both directions, which catches volatile loss going one way and oxidative gain going the other. The aged residue is then put back under the penetration needle at 25 °C to T 0604 and the result divided by the original figure — that quotient, as a percentage, is the 残留针入度比.

为什么最硬的牌号要求最高的保留率 · Why the hardest grade carries the strictest retention floor

Across the JTG F40-2004 A级 grades this page states, the requirement runs 63 % at 50#, 61 % at 70#, 57 % at 90#, 54 % at 110#. Read from the soft end that looks like softer grades being let off lightly. Read from the hard end it is the more interesting statement, and it is the one that matters here: the harder the grade, the less it is permitted to harden further.

The first reason is arithmetic. A 50# starting at 40–60 dmm and retaining 63 % lands at roughly 25–38 dmm after ageing. A 70# starting at 60–80 dmm and retaining 61 % lands at roughly 37–49 dmm. Even at the stricter percentage, the aged 50# is materially harder than the aged 70# — and 25 dmm is approaching the region where a paving binder stops relaxing thermal stress usefully at all. The percentage is tightened at the hard end precisely because the absolute residue has so little margin left. There is nowhere for it to go.

The second reason is compositional. A 50# is already the product of a more severely processed vacuum residue than a 70# from the same crude slate. It carries proportionally less of the light maltene fraction that a thin film at 163 °C strips out. A binder in that condition should not be losing a large percentage of its penetration in the oven, and if it does, that generally points to something other than ordinary ageing — residual cutter, a blend that has not stabilised, or over-blowing. In practice, therefore, the 63 % line does double duty: it is a durability requirement and it is a process-integrity screen.

为什么这一行在50号上最值得看 · Why this line deserves the most scrutiny on a 50# COA

50# was chosen for stiffness, which means the risk on this grade points the opposite way to the risk on a soft one. Excess hardening in the plant does not cost a 50# its purpose; it overshoots that purpose. The layer goes down stiffer than the design calculated, and the one exposure the grade was already carrying — cracking — is enlarged before the road has taken a single truck. There is no headroom left to spend. On a 50# Certificate of Analysis the retained penetration ratio is the line to read first, ahead of penetration itself.

One conversion trap belongs specifically to a hard grade. Export certificates built to an ASTM habit often carry this line inverted, as a permitted drop in penetration rather than as a retained fraction, and the inverted form flatters itself against a 63 % floor because the two are arithmetic complements — a drop of no more than 20 % is a retention of at least 80 %. On a 50# that comparison decides very little, because a permitted drop is a ceiling written across a whole grade family while the thing that governs a stiff pavement is the absolute residue in dmm. A parcel entering the oven at 42 dmm and leaving at 27 has retained 64 % and passed; the identical 64 % on a parcel entering at 58 leaves 37, and those two residues do not behave alike in a winter. Ask for the measured before-and-after pair in dmm alongside the ratio, run under the ageing procedure the contract names and reported in the Chinese form, and read the residue rather than the percentage.

蜡含量 · Wax, and why it bites a hard grade at both ends

蜡含量 is determined by distillation under T 0615, and the ceiling moves only with the class: 2.2 % at A级, 3.0 % at B级, 4.5 % at C级. It is the single line on which most imported material loses a Chinese enquiry, and the point is worth putting bluntly rather than routing around.

Take the market position before the chemistry, because it sets how much benefit of the doubt an imported hard grade will be given. China refines the great bulk of the bitumen it uses, and nothing about a 50# enquiry indicates a shortage; a cargo arrives because import logistics beat inland freight into a coastal project, because a window opens in price or quality, or because a project wants something the nearby supply cannot conveniently produce. An imported 50# offer is therefore never assessed in the abstract. It is put beside a domestic hard grade drawn from a naphthenic crude slate, naturally low in wax, whose wax result the buyer’s laboratory has seen many times over and expects to be unremarkable. Many Middle East crudes run more paraffinic and carry more wax through into the residue, and that compositional difference — not price, not paperwork, not relationship — is the largest technical obstacle to Middle East bitumen reaching a Chinese A级 acceptance. No commercial argument removes it, and 50# is the worst rung on the ladder on which to discover it, for the reason set out next.

For a hard grade the damage is two-sided, which is what makes it worse here than anywhere else on the ladder. Crystalline paraffin wax softens the binder at high service temperature — surrendering exactly the deformation resistance the project paid for when it specified 50# — and stiffens it at low service temperature, at the end where a 50# already has the least margin. It is also associated with 泛油, bleeding to a slick surface in hot weather, and it can weaken adhesion between binder and aggregate. A high-wax 50# gives away its summer advantage and worsens its winter exposure at the same time. It is the one contaminant that attacks both sides of the trade-off this grade is built on.

没有B级退路 · The fallback that usually does not exist at 50#

On other grades, a wax result between 2.2 % and 3.0 % has an honest commercial route: offer the material for a B级 application, where 3.0 % is permitted. At 50# that route is usually closed. The projects that specify a hard grade are high-class roads under heavy traffic, and the layer that needs the stiffness is the surface or middle course of an expressway or class-1 highway — the position from which B级 is excluded. So a 50# cargo that fails 2.2 % has generally failed for the application, not merely for the class.

Two procedural points follow, and both are sharper here than on a softer grade. First, the wax figure has to come from T 0615 run on the parcel actually being offered. EN 12606-1 is also a distillation determination but it is not the same procedure, so a European result should not be presented under a T 0615 heading; and a figure carried over from an earlier production run is evidence about that run, not about this one. Second, because the 50# application closes the B级 route described below, the wax number drives a binary decision rather than a graded one — the parcel either serves the enquiry or it does not. That makes the timing the whole game: establish it before the offer leaves the desk, not once the vessel is on the water and the only remaining options are a discount or a rejection.

两条容易漏掉的线 · Two more lines to request explicitly

The 针入度指数 window is -1.5 to +1.0. PI is not a directly measured quantity — it is derived from penetration run at two or more temperatures — which is why it is absent from most Middle East export certificates: nobody ordered the second temperature. On a grade whose whole case rests on temperature behaviour, that is a conspicuous gap, and it belongs in the pre-shipment test schedule rather than in a destination laboratory’s findings. And ductility for 50# is specified by class and climate zone at 10 °C and 15 °C, not at the 25 °C that appears on most export data sheets. A hard binder has less ductility inherently — that is what hardness means — so this is not a formality that a comfortable 25 °C result covers. Have the test run at the temperature the standard names, and read the required figure out of the 50# column rather than borrowing the 100 cm that applies at 70# and 90#.