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A practical resource for refinery technologists and laboratories of road-construction companies that have received a technical brief to produce polymer-modified bitumen of class PMB 45/80-65 and are selecting an SBS rubber. No marketing — just concrete figures, formulas and references to DSTU.

PMB 45/80-65 is the most widely used class of polymer-modified bitumen in Ukraine for category I–II roads. Its quality is 50–60 % determined not by the SBS grade itself, but by how the rubber architecture, styrene content, dosage and incorporation technology are selected. Below is a complete working algorithm: from reading the class designation to a selection checklist and laboratory control of the finished binder.

1. What PMB 45/80-65 is and why SBS is needed

PMB 45/80-65 is a polymer-modified road bitumen with a penetration of 45–80 (0.1 mm at 25 °C) and a ring-and-ball softening point of at least 65 °C, produced in accordance with DSTU EN 14023:2023 "Bitumen and bituminous binders — Specification framework for polymer modified bitumens".

The designation reads as follows:

• 45/80 — the penetration range per DSTU EN 1426. The higher the number, the softer the bitumen at +25 °C: for PMB 45/80-65 this means 45 ≤ penetration ≤ 80 (0.1 mm).
• 65 — the minimum softening point per DSTU EN 1427 ("ring-and-ball"), in °C. This is effectively the lower limit of thermal stability — below 65 °C the finished PMB must not "flow" under the hottest summer conditions.

Base bitumen (for example, BND 70/100 per DSTU 4044:2019) has a penetration of 70–100 and a softening point of about 43–51 °C — it will not meet the PMB 45/80-65 specification without modification. SBS rubber is added precisely to raise the softening point by 15–25 °C, lower the Fraass breaking point by 10–15 °C, increase elastic recovery (for PMB 45/80-65 — a minimum of 50 %) and stabilize viscosity at high laying temperatures.

SBS is a thermoplastic elastomer with polystyrene and polybutadiene phases. In bitumen, the polybutadiene phase swells, forming a microscopic elastomeric network that gives the PMB elasticity at low temperatures and rutting resistance at high ones. Without SBS, the PMB 45/80-65 class per DSTU EN 14023:2023 cannot be achieved; alternatives (EVA, crumb rubber) deliver a different property profile and belong to other classes.

2. PMB classes per DSTU EN 14023:2023 — how to read the designation

DSTU EN 14023:2023 governs the designation of PMB classes by the penetration range of the base bitumen and the minimum softening point of the modified binder. In road practice the following designations are the most common:

How DSTU B V.2.7-135:2014 relates to DSTU EN 14023:2023. The older sectoral DSTU B V.2.7-135:2014 "Polymer-modified road bitumens" is still valid in parallel and defines the grades BMPD 60/90, BMPD 60/90-2, BMPD 80/120, BMPD 90/130. The PMB classes per DSTU EN 14023 are a broader and more detailed designation; a manufacturer may state both markings (for example: "PMB 45/80-65 / BMPD 60/90-2").

A softening point of PMB ≥ 65 °C critically depends on the SBS concentration (3.0–4.5 % by mass for PMB 45/80-65), the SBS architecture (linear vs radial), the styrene content (28–32 % for class 45/80-65) and the state of the dispersion. Failure to meet even one parameter = failure to meet the class. This is the main cause of rejects: supposedly "the right SBS was bought", but the dosage or technology were not fine-tuned.

3. Linear SBS vs radial SBS — which to choose for 45/80-65

SBS rubbers are distinguished by molecular architecture: linear (triblock S-B-S) and radial (star-shaped (S-B)ₙX).

The rational choice for PMB 45/80-65 is a linear SBS with a styrene content of 28–32 %. This is the optimal balance of price/quality/processability. Radial SBS delivers higher figures but raises the PMB production cost by 6–10 %, requires a longer mixing cycle and carries an increased risk of segregation during prolonged storage of the finished PMB (over 72 h) — which is critical if the binder is dispatched slowly.

Exception: if the customer's specification explicitly requires elastic recovery ≥ 65 % (for example, for category I-A motorways with traffic exceeding 6 000 vehicles/day), a radial SBS or a blend (75 % linear + 25 % radial) is worth considering.

4. Styrene content 30 % vs 40 % — how it affects properties

The SBS molecule consists of polystyrene blocks (S, hard, Tg ≈ +95 °C) and a polybutadiene block (B, elastomeric, Tg ≈ −95 °C). The polystyrene phase forms physical cross-links that hold the elastomeric network within the bitumen. Hence the rule: the higher the styrene content, the stiffer the network, the higher the moduli at high temperatures, but the lower the low-temperature elasticity.

Class PMB 45/80-65 simultaneously requires a penetration of 45–80, a softening point ≥ 65 °C, elastic recovery ≥ 50 % and a Fraass breaking point ≤ −15 °C. A linear SBS with a styrene content of 30 % at a dosage of 3.0–4.0 % by mass usually brings all four parameters into spec at once. High-styrene (≥ 35 %) can "pull" the Fraass into the undesirable −10…−12 °C range — the PMB will pass the upper specifications but fail the lower ones. High-styrene SBS is a tool for the PMB 10/40-75 class (bridges, runways).

What to avoid: mixing SBS 30 % and 40 % "on the fly" without laboratory selection (chaotic batch parameters); using soft SBS (< 28 %) for road PMB (this forces overdosing > 5 % and provokes segregation); relying on marketing promises of a "universal SBS" — each PMB class has its own optimal styrene range.

5. SBS dosage in bitumen — formulas and reference values

A correctly selected dosage simultaneously determines both attainment of the target class and the batch cost. An error of 0.5 % SBS on a 30-tonne batch = ±150 kg of rubber in direct costs, plus either a missed class or a "saturated" curve where a further increase in styrene achieves nothing.

For class PMB 45/80-65 based on BND 70/100 or BND 60/90 bitumens, the working window for a linear SBS with a styrene content of 30 % is 3.0–4.0 % by mass of the bitumen, with a typical value of 3.5 ± 0.3 %. The stabilization point is not a pick from a price list but the result of laboratory selection for a specific batch of base bitumen: different refineries (and even different batches from one refinery) have a different propensity for swelling of the SBS phase because of differences in the maltene fraction.

Formula for a reference selection (the laboratory's starting point):

where T_target is the target softening point (DSTU EN 1427); T_base is the softening point of the base bitumen; k is the empirical increment coefficient: ≈ 6.5 °C/% for linear SBS 30 % and ≈ 7.5 °C/% for radial.

Example (PMB 45/80-65 on BND 70/100): T_base = 47 °C, target T ≥ 65 °C, ΔT = 18 °C → dose = 18 / 6.5 ≈ 2.8 % of linear SBS 30 %. This is a starting point, not the final dosage: the laboratory prepares three samples around the calculated point (2.8 / 3.2 / 3.6 %) and measures the full property package. The batch goes into production only when all parameters fall within the class window simultaneously.

To combat segregation during prolonged storage (over 72 h at 180 °C), polyphosphoric acid (PPA) is used at a dosage of 0.15–0.30 % by mass — it cross-links the SBS domains with asphaltenes and reduces the difference in phase densities. PPA does not replace a quality SBS but merely widens the technological storage window.

What not to do: exceeding 5.0 % SBS (the increment curve saturates already at 4.5–5.0 %, while segregation rises sharply); economizing down to 2.0–2.5 % on "warm" bitumens (the formal class may be reached, but elastic recovery drops below the minimum); replacing linear SBS with radial without recalculating the technology (radial has a 15–25 % higher viscosity at the same percentages).

6. Incorporation technology (high shear mill vs propeller mixer)

One and the same batch of linear SBS 30 % can yield either an in-spec PMB or a segregated reject — depending on how it was dispersed.

High shear mill (colloid mill, rotor-stator) — the industry standard for granulated SBS. The base bitumen is heated to 175–185 °C, the SBS is fed into the stream through a doser, and the mixture is pumped repeatedly through the mill. Operating parameters: rotor speed 4 000–6 000 rpm; rotor-stator gap 0.15–0.30 mm; dispersion time 25–45 min down to an SBS particle size ≤ 5 µm; maturation 1.5–3 h at 175–185 °C with low-speed stirring. The high-shear field "tears" the granules down to a sub-micron dispersion — it is precisely this that yields a stable PMB capable of withstanding storage of over 72 h without stratification (control per DSTU EN 13399).

Propeller mixer (blade agitation) — an ordinary bitumen tank with an agitator (60–120 rpm) at 180 °C. Suitable primarily for powdered SBS, which dissolves faster than granules. Duration 4–6 h. Capital costs are roughly 90 % lower, but the dispersion quality is worse and the segregation risk higher. This route is chosen by small producers or where PMB is made to order and dispatched immediately.

The quality of SBS distribution is checked by fluorescence microscopy (the polymer phase glows under UV) or indirectly — by the storage stability test per DSTU EN 13399. The two most common mistakes are too low a temperature (< 170 °C — bitumen in a "gel" state does not allow the polymer to swell) and too short a dispersion time (undissolved granules are visible to the naked eye on a glass sample).

7. Laboratory control of the finished PMB — critical parameters

Finished PMB 45/80-65 is not considered as such until the laboratory has confirmed the full package of six parameters simultaneously. None of them is self-sufficient.

1. Penetration at 25 °C — DSTU EN 1426 (needle 100 g, 5 s). For class 45/80-65: 45–80 (0.1 mm). Below 45 — over-modification; above 80 — insufficient dosage.
2. Ring-and-ball softening point — DSTU EN 1427. The key class indicator: ≥ 65 °C. The most sensitive to SBS concentration and architecture.
3. Elastic recovery at 25 °C — DSTU EN 13398. An indicator of a formed elastomeric network: a minimum of 50 %, and for a "living" road PMB preferably 60–70 %.
4. Fraass breaking point — DSTU EN 12593. Control of low-temperature behaviour: ≤ −15 °C for class 45/80-65.
5. Storage stability (segregation) — DSTU EN 13399. The sample is held for 72 h at 180 °C in a vertical tube; the difference in softening point between the upper and lower parts must be ≤ 5 °C.
6. Dynamic viscosity — DSTU EN 13302 (rotational viscometer). Control of processability: too high a viscosity complicates pumping and spraying, too low signals insufficient modification.

In practice the manufacturer keeps a record for each batch, in which all six parameters are consolidated into a single table with the tolerances of class 45/80-65; the batch is shipped only on condition that no indicator falls outside the window. This is precisely the difference between certified PMB and "bitumen with rubber".

8. SBS selection checklist — a practical decision table

A consolidated matrix as a reference for starting the laboratory selection (the final dosage is always refined on the specific batch of base bitumen):

A brief selection algorithm for PMB 45/80-65:

1. Determine the grade of the base bitumen (BND) and measure its T_base.
2. Choose a linear SBS with a styrene content of 28–32 %.
3. Calculate the starting dosage using the formula dose = (65 − T_base) / 6.5.
4. Prepare 3 samples around the calculated point on a high shear mill.
5. Check the full package of 6 parameters (section 7).
6. If storage stabilization is needed — add PPA 0.15–0.30 %.
7. Record the formulation in the batch report.

5 questions worth asking before selecting an SBS

1. Linear or radial SBS for 45/80-65? For the universal class 45/80-65, in the overwhelming majority of cases the rational choice is a linear SBS with 28–32 % styrene: it delivers the required parameters at a lower cost and with better resistance to segregation. Radial is warranted when the customer explicitly requires elastic recovery ≥ 65 % or for hard classes (bridges, airfields).

2. Why does the "right" SBS sometimes yield a PMB reject? Most often the cause lies not in the rubber but in the dosage or dispersion: too low a mixing temperature, too short a time on the high shear mill, or the absence of a maturation stage. The SBS may be perfect, but without a sub-micron dispersion the elastomeric network does not form.

3. How much SBS to add — can it be done from a price list? No. The starting dosage is calculated by the formula dose = (T_target − T_base)/k, but the final value is confirmed in the laboratory on the specific batch of base bitumen. Two batches of "3.5 %" from different refineries can differ by +3…+5 °C in softening point.

4. Why is polyphosphoric acid (PPA) needed? PPA (0.15–0.30 %) widens the technological storage window of the finished PMB by cross-linking the SBS domains with asphaltenes and reducing the difference in phase densities. It does not replace a quality SBS and does not raise the class — it merely insures against stratification during prolonged storage in the tank.

5. How to make sure the finished PMB meets the class? Check all six parameters simultaneously: penetration (EN 1426), softening point (EN 1427), elastic recovery (EN 13398), Fraass (EN 12593), storage stability (EN 13399) and dynamic viscosity (EN 13302). Compliance on just one or two indicators does not mean the class has been achieved.

Summary

Selecting an SBS for PMB 45/80-65 is a sequence of four fine-tuned decisions: architecture (linear for the universal class), styrene content (28–32 %), dosage (3.0–4.0 % with laboratory refinement) and incorporation technology (high shear mill down to ≤ 5 µm). Each link affects the final package of six parameters of DSTU EN 14023:2023. Quality raw material is a necessary but not a sufficient condition: the PMB class is born at the intersection of grade, formulation and technology.

Need SBS for producing PMB 45/80-65? Exaflex® SBS 7090 — a linear rubber with a styrene content of 30 %, compliant with DSTU EN 14023:2023, with a CoA for each batch and dispatch from the warehouse in Derazhnia. To buy with delivery across Ukraine or to select a grade for your base bitumen — consult a Material Wizard specialist.